As natedog pointed out, Glock rushed to get into the .40 Smith and Wesson market by making minimul modifications on their 9mms. The Glock 20 was built from the ground up to be a 10mm and everything about it was engineered to take a steady diet of full power 10mm Auto and outlast its owner. It is very durable and surprisingly comfortable to shoot. If you haven't experienced a Glock 20 loaded with Double Tap, you're missing out, IMO.
Glock barrels are pretty high quality. Their chambers are cut loose as a reliability measure but even with the loose chambers, I've seen some pretty good accuracy. And Glocks don't have unsupported chambers either. The feed ramp removes a tiny fraction of an inch from the 6 o' clock position but other than that the Glock offers support on par with most other brands I have seen. Comparatively, the barrel from my Glock 20 is very similar in design to my HK USP 45 barrel, just looser and with a little less support at the 6 o' clock.
I don't really see what the big deal is. If you shoot strictly factory ammo, shoot and be happy. If you want to handload and hover near the upper end of a cartridge's potential, and you feel a new barrel might be safer and extend case life, get one. The Glock is fully on par with name brands like SIG and HK in terms of quality and even with the aftermarket barrel, isn't going to cost any more than them.