Whats the point in the different size phones if you can just stick a memory card in it anyway?
With many games hitting between 1-2GB in size, 16GB can fill up in a matter of days. I think you have to be rooted to move game data to the sd card and a lot of people aren't. Saying that though, I'll be surprised if we even see a 64GB model at all, did the 64GB S3 or Note 2 ever see the light of day?
I'll be watching with interest what the S4 has to offer because my next phone will most probably be the Note 3. A 64GB version with a 64GB sd card would be very nice!