Can someone fill me in on why the gap is so much better?
I don't think its "so much better". From what I have read the 45 GAP has simular ballistics to the 45 ACP in a little smaller gun. A lot of people complained that the G20 (10mm), G21 (45 ACP), G29 (10mm) and G30 (45ACP) were to big (wide, thick). But people still wanted to use Glock's and the 45 ACP (even the 10mm) for obvious reasons! The 45 ACP is a great cartridge (as is the 10mm).
I have two Glock's a G22 and a G27 both 40 S&W. I want to get a 9mm either a G17L with a 6 inch barrel or a G34 with a 5.3 inch barrel for plinking. I also want to get a G20 in 10mm. I wouldn't mind a G21 in 45 ACP. The full size Glock's fit me pretty good. I know my wife wouldn't be able to shoot them. There just to big!
I think if the law enforcement community starts to use the 45 GAP then it will be a success. If not, I'm not sure. The law enforcement community is what made the 40 S&W as popular as it is today!