No one ever asked for a boss fight. Hell, I'm glad the Illusive Man boss fight was cut, because it would be a total betrayal of his character.
The whole lack of Harbinger boss battle thing, is because it would fit Harbinger's character and it felt what having him as the villain of the entire Mass Effect 2 was building up to.
Bioware is not catering to anyone, only the story. If they had a longer production time, I bet they would have worked on a way better final level than take on some generic Reaper enemies that you've been fighting for the entire game.
I totally support the calls for a Boss Fight, especially against the Harbinger, because it would be a total sense of accomplishment.
I disagree that Bioware's current ending was 'deep'. It was provoking, but only in the sort that provoked anger and confusion. Sure, it sure as hell was mentally stimulating considering I had to think over and over about it for weeks until it finally made sense in my mind.
It was a rush job, and a failure though. I would disagree that Bioware cut the Boss Battle out of attempting to create a 'deeper' ending. They cut out any final battle just to shove in the abrupt ending that we received.
I personally did not like the final Illusive Man confrontation. Lack of music, combined with a terrible ambiance. The writing was good, but it still felt like a betrayal of TIM's character and a terrible plot point that we already saw coming miles away. Then add onto that after the elevator to heaven, and the entire ending went down the drain.
Including a boss fight has nothing to do with the quality of an ending. Look at the ending of Knights Of The Old Republic 2. The final battle was the ending, and it was a very wonderful scene involving the student against the mentor. Again, it was rushed by an impatient publisher and left us without conclusion, but we actually felt like we had accomplished something in the end.
The connection between having a boss fight and 'deep' meaningful endings is false. Maybe you believe Mass Effect isn't just one of those story's that climaxes in a final battle, but a majority of fans believe that we should have received some form of a brilliant climax.