It would take more than hover states for UX designers to be able to treat mobile devices like desktop ones (and failing to celebrate their differences could be considered a mistake).
To understand why, we have to define the terms and then consider the differences.
Defining the terms
What do we mean by 'Web' interaction and what might we mean by 'mobile' interaction? First, let's use 'desktop' instead of 'Web', because it's more specific, and because I suspect it's more in line with what you meant when you posed the question.
With the advent of tablets, desktop touchscreens, desktop OSes that borrow from touchscreen OSes (i.e. Mac OS X Tiger), and experimental interfaces such as 10gui, I would argue that the line between 'mobile' and 'desktop' is blurring, and that it may one day cease to exist. As such, one could argue that the question we should be asking is "what advances in desktop hardware and software are required for UX designers to be able to treat desktop interactions more like mobile ones?", but I'll set that aside for the time being.
Instead, let's define our spheres of interaction as follows:
Mobile: An interaction that takes place on an untethered, highly portable touchscreen device. This includes phones and tablets.
Desktop: An interaction that takes place on a (usually) tethered, less portable device with a monitor and a physical keyboard. This includes desktops and laptops.
The differences
Is a lack of a hover state the only thing that separates these areas of interaction? We quickly see that this isn't the case; there are a vast number of additional considerations that apply to mobile design that don't apply to desktop-based interactions:
Hit areas for mobile need to be bigger. Interaction is defined by a finger, not a pointer, and so interface elements often need to be bigger in order to be usable.
Mobile interactions often take place in a shorter or more fragmented time frame. The experience of using a desktop computer, by way of the fact that you're often sitting at a desk, puts interactions in a slower, more considered time frame than a mobile user moving from place-to-place. Mobile interfaces often have to be more obvious, with less room for clutter.
Mobile interactions regularly occur in a much wider range of lighting environments. Desktop environments often have fixed or controllable lighting conditions. Mobile interactions can take place anywhere, and UX engineers would be wise to consider this.
Mobile interactions continue to be subject to stricter bandwidth considerations. When dealing with network communication, mobile devices are limited by bandwidth considerations and dropped connections more than their desktop counterparts.
Mobile screens use gestures. Although gestures are making their way to the desktop, a mobile application that doesn't consider gesture-based input as a means of interaction often feels rushed or unconsidered.
Mobile screens have multiple input points. Multitouch enables mobile interactions that aren't possible (or that don't feel intuitive) on a desktop. To ignore gestures such as pinch-to-zoom when they're appropriate just to unify a desktop and mobile interface would be a mistake.
Would a hover state on a mobile device even work the same way as a desktop one?
I'd argue not.
If we think of a mouse pointer as a finger that's at a constant fixed distance from the screen, we can quickly see why a hover state is useful on the desktop: to move the pointer from one area to another, it has to move through every object in between, which activates any hover states. This is why it's often considered 'safe' to convey additional information in hover states on desktop devices that use mouse pointers; there's a good chance the user will activate them because they're doing it all the time without even meaning to.
But it wouldn't work like that on a touch screen. If you watch a user operating an iPad, for example, they won't typically hover their finger over the screen when moving their finger between two or three separate points. Interactions take place as isolated taps and gestures. People track on a monitor but peck on a touchscreen, because a finger is so much more liberating than a mouse, and because suspending your arm over a screen isn't natural.
In order to get information about an element through its hover state on a touchscreen, a user would have to actively decide to hover her finger over it. It would be unwise, perhaps, to seek to embed additional information in hover states on a touchscreen device, because there's less chance that they'd be activated. And so it's likely that we, as UX designers, would not be able to use hover states on mobile devices in the same way that we use them on desktop ones even if they did exist.
Would desktop-style hover interactions translate well to mobile screens?
Additionally, I would posit that hover states could prove incredibly frustrating on a touchscreen device. Consider a navigation menu that pops up upon hover and presents a list of links. With a mouse, it's fairly easy to hover the pointer over a fixed point, move it down the list, and click an item. Consider the same gesture on a touchscreen: you must first hover your finger over the nav area. To click the fifth item down the list, you must now move your finger down four elements, keeping it at approximately the same distance from the screen, without moving it closer to the screen to tap items one-to-four by accident, or further from the screen to deactivate the hover state. Frustrating? I think it may prove to be, although user testing would be needed to confirm this.
Simply put, hover states wouldn't be as obvious on touchscreens, and the sorts of hover interactions we're used to on the desktop may not translate as well to touchscreen devices. I'd argue that, even if they did exist, hover states on mobile devices would be far less useful.
In summary
Mobile and desktop interactions are different in many more ways than just hover state. For now, these differences should be celebrated as an opportunity to delight the user, not as an inconvenience. In the future, it's likely that the convergence of 'mobile' and 'desktop' will cause us to come back and redefine the two terms; with luck, we may find that they've taken on the same meaning.
