As all the rumor sites (e.g., WSJ ;-) are predicting, it'll definitely have at least 512MB of RAM (can't imagine it having less than the iPhone 4).
But that's still pretty anemic, as jonhohle noted: that's not enough to keep a lot of pages in Safari's cache. (Though, from my experiments, Safari/WebKit is REALLY aggressive about minimizing memory usage, perhaps even stupidly.)
It's almost certainly about power consumption; Apple absolutely loves being able to tout huge battery life compared to the competition, and one way they do that i s by being tighter on things like RAM usage.
It's also worth pointing out that the RAM lives in a Package-on-Package configuration right on the CPU die. They're not exactly buying mass market SO-DIMMs and sticking them in a bog-standard bus, so the cost per MB is probably higher.
The processor and the ram are stacked on the same chip. So they're kinda limited as to what they can put in there. I doubt that you could fit a SO-DIMM of any stripe inside an ipad case, nor would you want the power problems.
But that's still pretty anemic, as jonhohle noted: that's not enough to keep a lot of pages in Safari's cache. (Though, from my experiments, Safari/WebKit is REALLY aggressive about minimizing memory usage, perhaps even stupidly.)