Actually we just completed the first year of the 64bit migration and I believe it went very well, next year will see plenty mre x64 boxes pushed out. At luanch time some vendors were stuck by dirver support (my kids HP IQ777 for example was 32bit since some needed drivers werent available at the time, now they ship it as a 64bit box).
Also remember, in less than 2gig scenarios 32bit is recommended (at least by me) since the physical code size is larger on 64bit machines. You wind up with less usable memory in the same situation (its always true, but once you get much past 2gig no-one will notice, and past 4gig you couldnt have used in on 32bit anyway).
Memory prices are one of the biggest drivers, 4 gig is still the sweet stop, but we are starting to see users move to 6 and 8 gig (I run 32 here). As 6 or 8 becomes 'standard' all of those boxes will be 64bit.
As an industry we don't change standards overnight, how long has it taken sata to replace pata? This migration requires (in my cases) a hw switch and an OS switch. I think we have a good 1-2 more yeas before you start seeing folks like my dad just get a 64bit box be by default.
(Oh and the last missing bit is 32bit to 64bit upgrade options in Vienna.....) I know plenty of people who would have upgraded for 4+ support (or at least to use that last 1 gig on their 4 gig system) if they could have upgraded in place.
Bill