As for the original problem...I avoid guns with rails like the plague, and I actually *build* holsters. (danddgunleather.com)
I don't think the Glock guy made a mistake at all.
Dave - I hear you on the rails, but even the Glock rep told me that the G21 & G30 are the same width and should fit in the same holsters. His explanation for why the G30 will not fit in the G21 holster without jamming it in and being very difficult to extract and why the G21 has no retention in the G30's holster was the holsters must be defective - go figure.
Oh well, over time I may attenuate my position, but I have been in the market for a high-cap 9mm. I was at my LGS showing off my Shield which I put XS sights on (big dot). They were opening some new shipments and I noted that the FN FS9mm had night sights. It appeared to be in between the G17 & G19 in size. Actually, it is shorter than either Glock (7.25 versus 7.36 & 8.03 for the Glocks), wider than the Glocks (1.33* versus 1.18) and .07 taller than the G17 and .46 taller than the G19. It also comes with 3 17 round mags and a pretty sweet trigger, which I understand gets even better with shooting (which happens to most guns regardless of manufacturer).
To make a long story short, I bought the FN. Now I have to find a holster for it and put a few rounds down range to see how it performs. If it performs as expected, I will have to get a few more mags for it. FWIW, the FN with factory night sights was about the same prices as the G19 without night sights and then there was a $50 mail in rebate to boot.
Well. after cleaning my new gun, I figured I would see how my X300 light fit on it. It slid right on just like on my G21 and other rail-equipped guns (except the G30).
* - The FN Web site says the width is 1.55, but my measurements show the widest part is the ambi safety at 1.33.