[Scene_Cast2]

Helicopter rotors are much more complex than just pitch control. Quadcopters fly fine with 1DoF pitch control - relatively easy and cheap to do, while helis have non-trivial 3DoF. Also, there are quadcopters with 1DoF pitch control, your comment isn't exactly clear whether you know about those.

[iano]

Yeah, sorry. Having cyclic pitch control on the 4 rotors of a quadrotor makes even less sense - then you really really might as well just be a helicopter.

There aren't a lot of quadrotors that use pitch control. That's half of their appeal; hook 4 brushless motors up to props and you're good to go. If you add in pitch control, then you either need 8 dof (4 motors, 4 pitch servos) or 5 dof (1 motor with a complicated power train to drive the 4 rotors, and 4 servos for pitch control). Both are more complicated and expensive, and again you might as well just be a helicopter.

[Scene_Cast2]

Yep, variable pitch quadcopters aren't very common, they're only used in (research-y) areas where stability is key (speeding up and slowing down propellers is slow compared to changing tilt). I agree that at this point it's approximately as expensive as a heli, just with different dynamics.

RE: Cyclic pitch on quads - I don't think anyone put cyclic pitch on quads before. I think I derived a way to make use of 13DoF for stability and dynamics that are impossible on a heli (hovering while tilting, moving back and forth without tilt, etc). PM me if you're interested in the idea, it's a little hard to describe in words.