People have been carrying on larger and larger bags for years. They think that if it has one of those little pull out handles, then it is a carry on.
Hey, if it fits in the little "test rack" at the ticket counter, it is a carry-on. I've been using one of those as my only luggage item since well before they started charging for checked baggage.
What ticks me off are the people who put multiple items in the overhead bin, like a bag, coat, etc, etc, and what ticks me off even more are the people who stop and put their bag in the bins near the front of the plane, even though their seat is in the back just so their bag is waiting for them at the front when the barge past everyone to get off the plane first. Like they're the only one who has a connecting flight. Air travel really seems to bring out the worst in people.