memory allocation in android

[centuryking]

kinda new to android so i was wondering if someone can clarify something for me.

how much percentage of the internal ram/rom does android require. it seems like it uses about 50% of your total ram and about 80% or your total rom leaving the user only a small amount to play with. let me elaborate....

for an htc desire (just as an example):
memory spec: 576 MB RAM and 512 MB ROM
actual available RAM for user: ~235mb (saw this from a youtube vid)
actual available ROM for user: ~120mb (saw this on gsmarena)

for an SE X10 (my phone):
memory spec: 1 GB storage, 384 MB RAM (im assuming the ram is part of the 1 gb)
actual available RAM for user: ~180mb (based on my handset)
actual available ROM for user: ~465mb (based on my handset)

based on these im just seeing a trend regarding the demand of memory from the android os. are these normal requirements from the os? if so, where are these resources being used? is it just me that thinks these requirements are ridonculously high? or am i totally just off on this whole thing?

any feedback on this would be greatly appreciated. im just going crazy trying to get clarification on this since i cant fine the info anywhere

thanks