I think it's extremely unreasonable to expect 8 GB ram, probably even 4 GB, for next-gen consoles. That money for this excessive amount of memory really is spent better elsewhere (or not at all).
4-8gb in 2010-11 is inline with the same memory budgets as X360\PS3 had. Its not exessive, its the same jump that was done last generation.
Especially when there are technologies (streaming, pixel shader and procedural textures, compression, tesselation) that let you work around memory limitations.
None of these technologies lets you completely work around memory limitations, and many cost a lot of resources, thus worse performance thus worse graphcis. 4gb is not excessive, i would say its the absolute minimum for a PS4\Xb3 that has good graphics in 2011.