All devices have Google apps on them, and phones without these are considered "lesser" and won't sell. (When's the last time your Android phone from a "big name" seller came without Google Play market?).

If so, they have access to a central repository - Google. Google could just refuse to give them the OS with Google apps unless the manufacturer/carrier pushed out updates. It would be in both party's interests to agree to do this - Google because it would stem the tide of insecure phones and the stench of dodgy apps being prevalent even in the official market; and for the phone manufacturer, updates and apps, and happy customers.

At this rate I am not going to get another Sony, that's for sure.

I owned only Nexii from 2011 on and I'm not even sure Google wants to update those thoroughly. They sacked 4.2 for Nexus S, 4.4 for Galaxy Nexus although they can run it (and they did with custom ROMs) just fine.

Last straw was the Lollipop update for the Nexus 5, where it turned out a perfectly working device into a nightmare with memory leaks, mobile radio drains and camera freezes, where a daily reboot was actually mandatory. Their bug report tracker is full of complaints, yet they didn't do anything and are casually talking about M. Sorry, I don't have to wait a year, then pray if my current device is going to be supported, or just cave in and get a new device the new Android revision will enter the market with.

So until customer experience becomes a priority, I'm not investing a single cent or a second of my time in Android.

That theoretical leverage only exists because of Android's ubiquity which it has because of the handset makers. We have no idea how long the contracts that stipulate that handset makers control updates is valid for but it's safe to assume that they are still valid today because the update/security fragmentation it creates is bad for everyone except handset makers. No doubt it's something that handset makers will hold onto for as long as possible because a lack of updates sells new phones.

Google is slowly breaking up the OS into applications that it can distribute in the app store which smells a lot like someone trying to get around a contractual obligation using a technicality. There are legal agreements between Google and handset makers that can't simply be dissolved by threatening to revoke access to the app store.