I've done a fair amount of traveling on several airlines: Delta, US Airways, Allegiant, Southwest, KLM/Northwest, TAP, Air France, Air Tran, Continental, Jet Blue, United, Virgin, Malev and I've never encountered any of them leaving wheelchair passengers hanging. I can't imagine that American (which I have somehow avoided but will be using next month to go to Oregon) or its regional contractors has a policy of being a dick to passengers that need accommodation.
I fly American a decent amount and I don't think they have materially different procedures than anyone else. They board all the wheel chair and other people needing assistance first, with assistance if requested, and then start the general boarding. The woman probably did not show up on time for the assisted boarding. I have seen gate agents in all airlines that are incredibly rude and inflexible, in part because they constantly deal with airline passengers who can be incredibly rude, stupid and demanding.
Also sounds like this was a short hop commuter flight and this is where you tend to find the C team or some partner airline operating things.