There is plenty that 10 mm ammo can't do...
10 mm is a fine round, but let's not get carried away. There is plenty that the 10 mm can't do. There are .357 magnum rounds that are more powerful than any factory 10 mm round. I wouldn't trust the Buffalo Bore .357 magnums for Bear or moose protection, so I sure wouldn't trust any factory 10mm round for those applications either. Especially not in such a light gun.
I would not depend on 10 mm to drop a charging Black Bear or Grizzly Bear with one bullet. I wouldn't be comfortable with 10 mm dropping a pissed off moose, either. If you have the time to unload all 15 rounds of your magazine into the beasties, then the Glock 20 will probably get the job done. The problem is that most dangerous animals aren't going to be very courteous. They'll get up in your face in a hurry. You might get one or two rounds off by the time that they are tearing you apart. The trick is to drop dangerous game before they injure, maim, or kill you. I've never been in one of these scrapes, thank God, but I've learned enough to know that you don't want to be undergunned in these types of situations.
Revolvers make better trail guns than autoloaders. The Glock 20 is a great gun, but it is not the perfect all-around gun. I'd argue that any .44 magnum, .454, or .460 revolver would be a better all-around gun. .44 magnums can shoot .44 special (very, very light recoil, great ballistics in +p) and .44 magnum as well. .454 revolvers can shoot very, very mild .45 colt, or extremely nasty .454 rounds. .460 revolvers can shoot .45 colt, .454, and .460 (even nastier than .454).
Sorry for the rant. I know that you were talking about autoloaders, not revolvers.
I like Glocks a lot, but I do think that Sig makes better quality autoloaders. I'd argue that HK does as well. It is hard to argue the overall package that you get when you buy a glock, but I voted other. I'd rather have a Sig or an HK.