The trouble is, once you decide to use the highest quality sounds, the best available samples, the most expressive keyswitching, well, even a GB is paltry. You look at the sizes of some of the better GIGA instruments, just ONE can max that GB out, and still need more!
lol... so what then, buy a keyboard with so little memory that you won't be tempted to load any sounds into it ?
I'd rather have 1GB that can be used for lots of different things than a tiny 64MB. There are countless libraries out there that would make excellent use of 1GB of RAM.