Does anyone know why apple only included 256MB memory?

The lack of ram means that in-memory cache for the browser is limited (to zero?), which limits performance.

The cost of ram seems so small (a few dollars per GB in bulk) to a software developer - is the cost energy consumption or ???

It's not RAM in the form of SIMMs or DIMMs, though, it's RAM embedded into the chip (like everything else; the A4 is a System-on-a-Chip), meaning that it's basically an L3 cache: it suffers from heat dissipation and placement issues just like the L1 and L2 caches do.

The real question is whether Apple has designed the A4 with an external memory bus that's currently not being put to use, and which would allow for future expansion in the "iPad 4G·S" or somesuch equivalent. It would actually be a very clever game-theoretic strategy to constrain the memory at first.

If Apple had instead released this first iPad without multitasking but with 2GB of RAM (or even more; it could certainly all fit in the case, and RAM doesn't really impact battery life) developers would be sloppy and use as much of it as they wanted, disallowing their apps from ever being multitasked in the future.

However, constraining memory to 256MB at first forces developers to write apps that only use that much. Later, Apple can release the 2GB model, and it would suddenly be possible to multitask 8 or more of the 256MB-model apps at once. (Of course, also making provisions for new "fat" 2GB apps.)

"A4 with an external memory bus"

I'm really completely out of my depth here, but if that were the case, I wonder if you could mostly eliminate the Flash memory, except for the OS. Would there be cost or performance advantages in doing so? I mean, it would suck to lose 64GB worth of stuff if the battery ever died, but the battery's locked in there, and you could put in some kind of backup button-battery... maybe that added complexity would negate any cost or performance advantages.

If the ram could be refreshed in this manner with only a button battery wouldn't motherboard manufacturers put them on normal computers and save the state of memory in case of power loss? That is a feature that I would like to have. on my MacBook pro that I put to sleep it will drain the large battery fairly quick. I think that refreshing the memory is actually a fairly power intensive thing to do in practice.

Besides being cheaper, flash memory is significantly more compact.

Oh... yeah, I guess that's right. I'm still thinking in terms of the old Palm devices that used RAM rather than flash. But that was a different time.

In integrated circuits, one usually implies the other.