Ah, but our atmosphere isn't pure O2, or even MOSTLY O2. Lots of nitrogen.
Who cares if CO2 leaks out a little faster... I don't know if it does, but CO2 is for emergencies. You should always use your floor pump (with a gauge) before every outing.
See my review of the CO2 system I currently use, for more info and the results I've seen:
http://kc-bike.blogspot.com/2007/05/...novations.html
And yes, I use BB gun carts for mine, and never had a problem.