Maybe it's more important to realise that the CPU and GPU in PC are connected in such a latency ridden, bandwidth starved fashion, that using the CPU is very ineffecient. And people upgrade their GPU's more often than CPUs, so even if your job runs 25% of the efficiency on GPU vs CPU, you may still have 10x the power on the table on that side if you're a PC developer and hence it will still make sense.
The next-gen consoles have their CPU and GPU linked in such a spectacularly better way, that making use of the CPUs actually makes sense.
However, that's not to say that many games are CPU limited rather than GPU limited. That's quite rare. And whichever way you look at it, if the cloud only has 3x the CPU power of an Xbox One, then of course that does not warrant stating, the Xbox One is as powerful as 40x 360, even by a long shot.
I personally think that it's more likely to be used for running processes that can continue while you're away from your Xbox. For instance, in Forza you can trade cars, paintjobs, parts and what not, and you could have this whole process running in the cloud for each user, and allow you to interact with it using Smartglass or a webbrowser, even just designing new logos and art for on your car using your tablet or PC, and then have the cloud components and storage make that available to you and/or other players in-game. That's not to say that you can't do something like that without Microsoft's brand of Cloud setup, but there are definite advantages of having bits of such hardware reserved per user.
And of course you could easily expand this to extended save-game systems for other games as well, for instance a Skyrim style RPG could save all world state that has changed through your interaction with it, and add background processes that keep the world in flow even during your absence. I think there's a lot that can be done with this, and there could be some definite advantages if developers can get a standardised API for creating and supporting such features that are tightly integrated with Microsoft.
However, another question I have not seen answered is if these would be available for Gold users only, or for Silver as well? Business wise it would make a lot more sense if this was Gold only - it would be relatively easy to hook up such server-side components to online game experiences. But that also means that points about giving the Xbox a lot more power in general would be a little misleading.
And for multi-platform developers, I would suspect they would be strongly inclined to provide their own servers for this purpose, so that they could provide such features to all the platforms they choose to support, in whatever way they want to.