It takes a lot to hit that RAM barrier on iOS with code. Yes 64-bit code takes up more space than 32-bit code, but the majority of memory is not used for code. It is used for images etc. -- Most apps do not use large amounts of memory for pointer intense structures or contain tens of megabytes of code.

Also, 64-bit addressing may be "meaningless" today if you disregard memory mapping of content (into virtual memory), but , as stated in the review, the 64-bit architecture comes with couple of other improvements including increasing the # registers.