I can only base this on my 20 years experience in LE. At the times I had to draw my gun, for any reason, the only time I can remember of having the luxury of using both hands was on the range.
You always have something in the other hand, flash light, ticket book, mirror (for peeking around corners), door knobs, bandits, etc.
One handed shooting, strong and week hand is critical. At extremely close range shooting you don't have the luxury of time, plus you're gun is needs to be extended, and exposed if using two hands at 2-6 feet or so.
Its my opinion that weak hand shooting is just as important then strong hand shooting.
But to each his own. 95% of my pistol/revolver practice is done with one hand, right and left.