To explain the restriction issue:
A lot of this depends on the device.
Normally, responsive styling uses the width of the screen to set the width and layout of the page. This should mean that, when a device is rotated, the change in screen width between the portrait and landscape orientations triggers different layouts.
However, some devices declare their width as the shortest side of the screen whichever orientation it is in.
In order to compensate for this, some devices declare which orientation they are in - this can help a little but it gets complicates for devices of different sizes: the CSS needs to understand which device they are on and which orientation it is in just to work out the width of the screen. And, with the sheer number of devices out there and the rate that new devices come to market, that is simply a logistical nightmare!
This is why many developers will only fix those issues when specific target devices specified by the stakeholders.
As far as the usability issues are concerned: What you need to consider is the use case for the page you have. If your use case dictates a vertical linear progression then there's not much you can do but, if your use case is more flexible then it's usually a simple case of what fits on the screen in logical placements.
