EDIT: Nope,
I think I'm wrong!
I'm still very, very skeptical that MS will simply be able to bypass the carriers. So far only Apple has had that clout. Even Google doesn't have that kind of power with Verizon.... and Google pretty much made Verizon the smartphone powerhouse it now is.
Google could literally buy Verizon and still not be able to deliver Android updates directly to Verizon customers. It's not about having enough clout with the carriers! Its about OS policies/problems that Google is no longer at liberty to change.
On Android, you NEED the manufacturers to deliver updates, because they literally rewrite parts of the Android operating system to get it running on their hardware. Android device manufacturers also develop a LOT of the low level drivers. All the additions/modifications the manufacturers make get inherently intertwined with the basic OS (on the lowest possible levels of source code). What that means is that every Android handset model has it's own unique version of the Android OS, which is only upgradeable as a whole. Google can't do that. If they tried, they would instantly brick every Android device out there because they would reverse all the modifications made by the manufacturers. That is just how Android works. That is the price Android pays for having ultimate flexibility in hardware (anything goes). That is one of the reasons Microsoft doesn't allow manufacturers to fiddle around with OS source code and mandates standardized hardware.
For WP however, it is only about Microsoft's clout with the carriers. So far, Microsoft hasn't had much luck with that (at least not when it comes to representing their customers interests). We all know Microsoft claims to have update-policy-improvements on the way for WP8, but so far I haven't heard any details. I'm not as skeptical as you are though. I think we have good chances that WP8 updates will come directly from MS without carrier intervention. I'm still skeptical about manufacturer's firmware updates though.
One last thing:
Every WP7 and firmware update we ever received came from a Microsoft server. Microsoft just isn't allowed to distribute those updates without carrier authorization. If the carrier doesn't provide that authorization, then Microsoft is legally bound to withhold that update from the carriers network (unfortunately). That is how it has worked so far.