The main difference when it comes to iPhone models of the same generation is memory. The new 5S is rumored to have 32g, 64g, and 128g options ($199, $299, $399 respectively). My question - how is cost of memory determined? From 32g to 64g, there's 32 gigs in between and it costs $100; from 64g to 128g, there's 64 gigs in between yet the price increase is the same, $100. Is there some logic I'm not understanding? Thanks.