Well, some people don't actually need to upgrade from the base amount of RAM. I prefer it when Apple does it this way because it keeps the initial costs down, still gives the users the flexibility to upgrade (in this case to 2 GB), and doesn't try to sell people more of a system than they need. I suppose then there could always be the option of downgrading some components, but I find Apple's method acceptable.
I agree that most people end up upgrading their RAM anyway, but look at it this way. If Apple offered 512 standard instead of 256, guess what - you'd be paying more for the machine, and do you know how much of a premium Apple puts on RAM? I would prefer to get the bare minimum of RAM with my machine from Apple and purchase additional RAM at a significantly lower price from a 3rd party than be forced to buy more RAM for Apple which I know they will be charging me their premium on. Saving money is not a bad thing!