Keep in mind that the x86-64/amd64 architecture also added a lot of other architectural improvements (like additional registers) and the processors supported running unmodified native x86 code much, much faster than the 32-bit only processors of the time. 5 years ago, if you wanted the absolute fastest x86 machine possible your best bet was to get a dual Opteron (amd64) system and just put a 32-bit OS on it. Running actual 64-bit apps also showed a significant speed improvement, regardless of ram usage.

This performance improvement, more so than the ability to address more than 4gb of memory, is the primary reason for 64-bit processing becoming mainstream, in my opinion.