I've seen the "we can't do anything" routine quite a bit on Emirates, 2 stick out in particular.
First was when the guy in front of me sat down and reclined his seat fully. I asked the guy to put it forward, he just said "I paid my ticket, I can do what I want". I called the attendant and said 1) I had no space, and more importantly 2) surely as we hadn't yet taken off it was against civil aviation laws for him to have his chair back. They asked him and he said no, said to me they couldn't do anything and walked off! In the end, 5 minutes of me banging my fist on his seat every 2 seconds convinced him he wasn't going to get his sleep.
Next, was a Kuwaiti guy who refused his middle seat because he was going to be between 2 women, he just sat in the next row with his arms crossed scowling whilst the person whose seat he'd stolen went nuts as he'd lost his aisle seat. The staff made the poor guy who'd lost his seat seem like the bad guy when the reality is they just didn't have the guts to take on the Kuwaiti guy.
As someone above said, try that anywhere else in the world and after 20 seconds of polite asking the response would be "sir, you must move or we will call the police to escort you from the plane". Given the reputation Dubai has for zero tolerance from police, I'm surprised the staff don't use the threats more often. It may be down to the fact that many of the staff are young and don't want to take on conflict situations. For all the problems BA has, the one thing I'll give them is their cabin crew know how to get their way on a plane!