Yep, that would make a difference. And it's using system ram for textures and so forth. One version I looked at had 1GB ram, so thats not to bad. But, there may be a point in there where one version of those things might work and another one at a higher res would not as the load goes up.
In addition as Jim adds more and more items to the aquarium the hardware requirements will increase as well. So what might run now, might not in the future. Interesting info.