Desktop isn't dead, but...
Andrew, I certainly agree with your main point, but disagree that tablets are in trouble. For example, I own an iPad and a MacBook Air. Both are nearly as portable, but they have very different uses, strengths, weaknesses, etc.
And, this is a point Microsoft doesn't seem to get yet... a mobile device, regardless of size and processing power, is a different kind of UI experience with different purpose and application.
A desktop or laptop is always going to be more productive for a certain set of tasks. But, at the same time, a mobile device is going to be more productive, or especially, more appropriate for another. If I'm going to meet a client or business associate, etc. at a coffee shop for a conversation, I'm probably going to take my iPad. I typically don't need to take a lot of notes and can easily do so on a device that is much less socially intrusive (especially if the person I'm meeting has no device in use). Or, if I'm on a ride into the city on public transit, it's far easier to use an iPad or phablet than pulling out a laptop, no matter how small the laptop is. It's just a totally different kind of interaction.
Yes, the gap has been closed in a few major areas, between laptop and tablet that has impacted the rapid rise of tablet sales. I'd say that first among these is battery life. With more efficient processors and better batteries, it's much closer these days. That's one of the primary reasons I initially went tablet, as I needed more than 3 hours of computing time away from a power-source. The other is portability, though as an Apple user, I guess I've been kind of spoiled for many years in that regard. (Where my wife works, most of the company issued laptops stay in the office, while the employees have found 'hack' ways to use iPads, etc. because their laptops are true boat-anchors!)
But, that doesn't mean tablets are in any danger, just that maybe the initial enthusiasm was a bit much, and that people aren't going to replace a $600 device every couple of years. The other problem was that many of the Android tablets were so horrible, I'm sure there are a lot of people who got burned and now think tablets are fairly useless.
Another point I might take issue with is your comment concerning the enterprise. While true, the enterprise is going to become less relevant in the big picture of future business. But that's a whole other discussion.
Ultimately, I think there is a lot of room for desktops, laptops, tablets, and phones (phablets)... they each have their advantages and disadvantages. None of them, IMO, are going away or are in much danger. The big question is - if one were forced to only pick one or two (for economic reasons, etc.) - which would they choose? That will probably become the biggest driver of any kind of major shift.