[Coda]

2GB is enough to run Windows 7. I said that. But it is the MINIMUM for 64-bit (which is what most computers run these days). It's enough to surf the Internet, check e-mail, do homework, etc. But the Windows 7 experience is MUCH more fluid with 4GB, and games dramatically benefit from it. 6GB is starting to become the recommendation.

You can update the RAM just as easily as you can update the hard drive. The factors you're forgetting are the CPU and the video card. (Though on Intel-based systems they're sometimes on the same chip.) Those CAN'T be replaced in a laptop, and on desktops it's not always guaranteed to be replaceable either.