The problem isn't that OEMs are unable to modify the OS, it's that they do it badly.
I've owned four Android devices, and used a lot more. Three were Google branded, and were awesome. My current phone is an HTC Sensation 4G, which is awful. I don't know that I can blame Sense and HTC for all that sucks about this phone, but I miss my Nexus One pretty much daily. I'm eagerly awaiting the Nexus 4, because it'll only cost a little more than I can sell my Sensation 4G for, and will return me to living in a pure Google Android experience.
I want less OEM customization because the OEMs break the OS and make it less pleasant. Even if I couldn't sell my current phone to recoup some of the cost, I'd probably still buy a Nexus 4. The friction of using an unreliable and quirky phone has a cost that I consider too expensive. So, I regret buying a device that doesn't have a pure Android OS build, and I'm very unlikely to make that same mistake again.