I think one major difference between the two countries has had a significant impact on the two communities:
In the U.S., for many years MilSim-ish players were shunned away from rec-ball with comments like ("all those useless mods", "camo does no good", etc), and those folks ended up playing airsoft, at least for awhile. This doesn't even account for the folks that airsoft draws who simply want more realistic equipment.
In Canada, it's very hard to get good airsoft equipment, therefore a higher percentage of folks interested in MilSim-ish equipment, clothing, games, get into paintball and it's more accepted there as a result. Look at how magfed paintball is much more popular north of the border than it is down here.