Well, gate staff are often overambitious when it comes to preserving bin space, especially at outstations (NUE and LHR come to mind). Often they just apply blanket policies (anything with rails is a no-go), which is puzzling because it makes you wonder what those bins are for when the type of luggage that probably 80% of passengers use these days isn't suppose to go in there.

Most of the time DAA means your bag will be returned at the stairs, though on the E190 and some F70 destinations that doesn't always work and so you may end up waiting at the baggage carousel after all which defeats the purpose of travelling with hand baggage only in the first place.

My stance is: If the bag is legal size and weight the bag should be allowed in the cabin. It's not the passenger's problem that the airline chose an aeroplane that cannot accept all hand baggage in the cabin.