Well, Walther is obviously selling enough PPK's to keep them in production. That, to me, is a very oversized .380 but people buy them. So I really don't see the Glock's size being a detriment.
This is not new, Glock has made their downsized .380's for years.
With advances in ammunition and firearms' design, the .380 is much more viable than in years past. Yes, the 9mm is "better" but it also comes in a larger package. I have yet to see one I'd want in my pocket. A pocket .380 is an excellent choice when you don't want or need the bulk of a larger handgun. I carry my S&W Bodyguard .380 quite often, when a 1911 is not wanted or convenient. It easily slips into a coat or pants pocket and is much flatter than a J-frame. I've put probably 1000rds through it over the last two years and it shoots very well. Unlike a lot of pocket guns, the S&W has real sights, plus the integral laser. Paint can sized targets are easy prey at 25yds. I guarantee nobody wants to stand 50yds away and let me shoot at them.
