I would say no. First, how will they enforce it? The code is free and open source, anyone can take it and implement it as they see fit. They can de-prioritize search results, but that smacks of extortion. About the only thing they can do is refuse support or maybe drop Marketplace access, but loss of the Market is worse than fragmentation and with Amazon's AppStore in the mix people will just gravitate there.
Second, the vast majority of the people out there have no idea what version of Android they're using or probably even that they're using Android at all. Those who do care will quickly be able to determine which manufacturers give good support and which models get the attention.
Third, this doesn't fix the perception of fragmentation. It's not reasonable to assume that Samsung and Moto and HTC will all release new versions on all their <2 year old phones the second Google releases code. Even if it takes a few months to port everything to a stable codebase you're already seeing leaks for the next generation OS by the time it's out.
Most importantly, if I were a manufacturer building a device and trying to choose an OS and I was being told I needed to be locked into a two year support commitment for a throwaway smartphone/tablet/printer/toaster I'd lean towards WP7 where Microsoft will do most of the work for me. Android is nice in that anyone can do whatever they want with it - but they need to supply their own coders. It takes far less effort to build a phone for WP7 since MS is handling a lot of that end for you - it's what you're paying for.
Google can provide guidelines but it's hard for them to enforce rules. I think those guidelines should suggest that a device that's no longer going to be updated by the manufacturer should be unlocked for community to decide if they want to upgrade.
What can you do as a consumer? Homework. Take a look at the history of the manufacturer you're interested in. Ask questions in forums like this one to see which phones get updated and how long it takes. And if you buy a low-end phone, expect low-end support.