About the .380 round, I never could figure out why there are no "super-capacity" .380 handguns out there. I bet you could get 20-30% more cartridges in a magazine compared to 9mm. That means we really should be seeing 25 round, full-sized .380's. Now, that would be something I would be interested in!
481 is right, the 380s could hold as many as a 9mm could. Most 380s are marketed as tiny mouse guns, so they're made with single stack magazines. The Bersa Thunder Plus model has a 15rd magazine capacity, and I believe the Beretta 84 is a 13 rounder.