Developers are always bitching; if it's good they bitch, if it's bad they bitch. Most them justify it with the quality of their output though. By the sounds of that, it's almost like Sony were fishing for an excuse to lock away that much RAM, because honestly other than a couple of rare times, when have developer complaints ever been taken into serious consideration by console manufacturers?
The Home example you gave right there is extravagant, yes, but a waste of resources. Some of us just want to get through those sort of mundane actions as quickly as possible. If Sony really wanted to do that, why not just offer it as an (optional) downloadable app. You download it, and it accesses low-level system resources to enable that sort of OS functionality (I'm sure there's a paradox in this but someone more technical than I could figure that one out).
Only issue here is that you won't be able to play games requiring more than 4.5 GB of RAM with this set-up, but Sony could just allow you to disable it and get that RAM back, and presto, you can play those games now. It's an issue stemming down to the individual user, and that'd be something for them to decide on.
You decide you don't want it, fine. You can still get around to doing all that stuff with a less elegant UI, but at least you still have that extra couple GB for games that could use it.
A scenario like that would be so much better; you still theoretically give devs as much RAM as they could need (say the less elegant UI only requires 1GB), and for those who want a richer Home-like OS experience like that example of yours, they can download that functionality, but live with the fact they can't play some games using the extra RAM now reserved for the OS. Win-win for everybody.