bb ipsc has cost advantages over real steal ipsc, more than just on ammo. comparing the relative price of the guns, both on the high and low end, and airsoft is always cheaper.
there is also the availability factor. firearms are restricted to specifically designated ranges, while bb guns do not have that sort of limitations (noise, penetration) which means that it could be fired almost anywhere. [note that safety precautions including ipsc standards should still apply in order to maintain the structure of the game]
a minor point, but airsoft offers higher capacity magazine capabilities than canadian handguns. arguably it is closer to real ipsc than what is offered in canada, in terms of reloading.
that said though, there are good ranges and organized events. and anything we can do in a bb ipsc match, we can also do in real ipsc. certainly real firearms pose more issues which require increase practice and skill in order to excel at the sport.
A problem with airsoft ipsc is that most airsofters do not organize or are uninterested in ipsc events. I've only heard of a handful of games organized in the past 6 or 7 years. its just not very popular.
I noticed that cobra airsoft has every piece of gear one would need to start ipsc. granted it is all china clones but i managed to build a rig for about $100. i don't know what the quaility is like but i should have my order in 2-3 weeks (waiting on the belt that is out of stock).