Well from what your saying you said DDR ram is low cost
and yes you can up the RAM and all without changing the architecture
The problem is Nintendo started it's architecture with a different type of RAM (not DDR) so basically if you go for 2GB DDR2 it's not just upgrading it's changing architectures
and basically Nintendo isn't ready to make that move no one would really be willing to give up a library of games for their next console just so they can up the RAM and all...
Get it now?