There is actually quite an aftermarket modification market for the Glock; perhaps not quite as large as the 1911, but extensive nontheless, including aftermarket barrels, slide stop, magazine release, slide springs, triggers, et cetera. And it’s not quite a fair comparison, as most 1911s you’ll see today are “aftermarket”, i.e. manufactured by someone other than the original licensee (Colt Manufacturing).
From first hand and anecdotal experience I’d definitely opine that the Glock is a more robust design than the 1911; I’ve seen Glocks with a reputed 20k rounds fired through them still shooting tight service-grade groups out of the box (<5"), while most 1911s, especially Colt and WWII era guns will be sloppy loose. The massive modified Browning-style lockup with the huge overhead lug locking into the slide is definitely more robust than the swinging link design in the 1911, and despite criticism of the Glock being a “plastic” gun, I’ve never seen a frame break or tear apart, whereas frame cracking is common on well-worn 1911s. I’ve also rarely seen a Glock balk at any factory ammunition, whereas I’ve seen a lot of 1911 (albeit, most of them customized raceguns) that were especially picky about ammo or powder loads.
As far as 9mmP vs. the .45 ACP, while it is true that the best loads in both produce roughly the same one shot stop statistics from the Marshall and Sanow data (warning: PDF), by experiment and forensic history the .45 ACP has less of a tendency to get plugged up and not expand, and thus, achieves desired penetration (12-14") without such a risk of overpenetration. The .45 ACP shows better stats within SAAMI spec loadings across the range of JHP bullet weights (230, 200, 185 grains), while the best 9mmP performance comes from above-spec +P and +P+ loads with a 115 grain JHP. The king of the one shot stops is consistently, as silenus mentions, the .357 Magnum with a 125 grain JHP load; see again the Marshall and Sanow data (PDF). Note that no statistics are shown for the .40S&W or .357Sig, but anecdote and similarity would anticipate similar performance. Also, the data is presented as-is (effectiveness of shots to the torso and head) with no attempt to provide any correction for variances in specific physiological effects due to shot placement.
On the balance I would go with a heavier, larger diameter bullet to assure penetration, but the differences between premium defensive loads are less than the difference in skill between a good shootist and a mediocre one, which argues for more and better training rather than spending money and effort trying to select a perfect defensive load. The only other general observation that can be made is that hollowpoint bullets are clearly more effective than full metal jacket or roundnose bullets, which means fewer shots to incapacitate a perpetrator and incidentally less chance of overpenetration, which then argues for their use universally in any weapon that will reliably feed and fire them. And that is really all that can be said about the debate between 9mmP vs. .45 ACP and everything in between.
When it comes to defensive use (if it has to come to that) old reliable standards are often the best. I have a fondness for the Hi-Power myself, it being the pistol I first learned to shoot.
Stranger