This will seem like a bit of a insubstantial answer (kind of a dodge), so sorry in advance.
From what you've said, it seems to not completely adhere in a consistent manner, yes. This isn't an original complaint with respect to Google, either.
Perhaps this is because Material Design was targeted (at least originally) at non-desktop users, whereas the Material Design guidelines aren't (targeting developers reading from Win/Mac)? If anything, consider that the goals of showing pure Material Design in the wild may be better served with devised demo websites as opposed to within the guidebook on implementing it (although Google have had a real sporting go at the latter). I'd also be interested to see some information on what degree other Google products (Youtube, Gmail, etc.) are Material Design compliant on desktop.
Material Design is an attempt to define a design standard for mobile/tablet (and more recently desktop, via Chromebook and select Google sites, as well as new experimental features in Chrome as of May '16)) experience, interactions, behavior and styling.
At a glance, I'd say that this non-compliance you've encountered is a tacit acknowledgement that certain parts of material design aren't appropriate for/relevant for the desktop user/developer demographic, or would clash needlessly with already established norms and standards for interaction on these platforms (for example, perhaps Google found that transitioning (not popping) new pages into view was perceived as a negative thing on desktop, like hiding slowness?).
Scoping our focus down to the guidelines themselves, consider that the Material Design guidelines are probably most often referred to by users in the desktop web environment, as mentioned above, and that Google are therefore targeting developers. This means that they'd be trying to avoid jarring the user by being consistent with existing understandings about web interaction, as well as further trying to cater to developers, who are probably in a hurry and likely reside in a top bracket of competence on the broad scale of computer users. That said, the guidelines they lay out however are on how to best match with Google applications in Google's Android environment (targeting all levels of competency), where the standards are different. These are fundamentally different goals. At a glance, I'd say that Google has tried their best to show their standards at work in the guidelines, without alienating or irritating the reader.
Also remember that Material Design is still evolving to meet changing expectations; the rules aren't set in stone and perhaps these inconsistencies may eventually propagate in some fashion (caveats pertaining to platform, etc) to the guidelines. From the guidelines themselves:
This spec is a living document that will be updated as we continue to develop the tenets and specifics of material design.
Alternatively, perhaps Google felt that less was more, and that legislating how things must behave on each platform was beyond the scope of guidelines?
To lift the closing words from the first link to AndroidAuthority:
These are guidelines rather than strict rules after all and developers are still free to use whatever UI they like. Good design doesn’t mean blindly following rules but rather knowing when to bend or adapt those rules to different situations.
Overall, Material Design has helped our phones look more attractive
and cohesive and Google has done a good job of implementing it.