Anyway, its looking more like its true BUT its nothing for you guys to worry about. Sony is most likely being coy/conservative with the machine at the beginning of the cycle because they don't want to be "caught with their pants down" in regards to the OS - like with the PS3. Reserving a sizable amount of memory for future proofing OS and then some (which is available for devs to use), on top of 4.5GB is a smart way of going about it.
In the future, when the OS adjustments are done and dusted they can lift some of those restrictions.
Edit: Also remember that the PS3's XMB OS used 120MB of RAM, before it was shunk down to 50MB (60% reduction).