People have to realize that the 3.5 gb left, is used for game purposes as well (at least a good part of it), they are just not available directly in dev hands.
It's a question of how you manage your ressources and what the console is mandatory doing for you (as a dev) in way of audio streaming, caching, for example. On PS360 you had, relatively, more available ram but you had to use it for a lot of mandatory stuff for each game and often rewrite the same thing for different context. That's part of the whole "ease of developpement" thing.
For now having more ram is the least concerns of any dev, we are not to the point yet where you would like more ram to fit stuff, but more in the timeframe when you try to find some elegant/effective way to use all that new amount of ram. Having 4.5 GB is already about ten times what you were used to work with on PS3 and the system is offloading a lot of hungry memory workloads for you with the "system" ram.

Edit: I worry where this will end up in. Respect to happen has to come from both sides, it cannot be forced.

On topic, its believed sony is witholding RAM for possible future uses.