Yeah, that's the place where I saw it. (ton's of interesting stuff on that site. Did you see the sawn off CAR15?)
You are correct, Sorry, I didn't mean to make it sound like they are all modified like that. Just that some units use G17's. This one must have been part of a batch modified for some reason maybe testing. I also remember hearing a while ago that Glock actually modified some guns in this fashion (manual safety) while trying to get them accepted by some armed forces/police departments. I don't think any of them were ever mass produced though.