Well, honestly, I'm not expecting any significant discounts on the devices. But ~30% of accessories, voice plans, and data plans is not something I'd risk sacrificing by ordering via Apple instead of AT&T.
I've never had an iPhone, so I don't really know anything about how strong the glass is, but I'd rather not take any chances.
As for Apple's customer service, they've already been pretty fucking horrible for me. I've been using various iPods for the past 7 or so years, and I've never found their "genius bar" to be useful, efficient, or even all that honest. I had a hell of a time exchanging my 5.5gen iPod Classic a year or two after I brought it home, turned it on, and realized that it had a smattering of dead pixels. Not to mention their bullshit over-the-phone customer service that tried to charge me $35 just to fucking talk to someone when I last had an issue.