Mancboy... for eyars 1000' vertical seperation F245 - F290 was standard, and 2000' applied above F290. This was based on (as said above somewhere) an almost arbitrary decision that clockwork, pressure driven altimeters lost accuracy with increasing level... so at F290 someone decided to build in a bit extra for the wife and kids...
Now some might suggest RVSM is the result of better equipment, others might say its a way to cramm more aircraft into the airspace... I think it's probably a bit of both, but with the imperrative definitely coming from the latter.
It's not unusual for operational pressure to be relieved by relaxing the rules!!!