[hla19]

Brushless motors are more expensive. There are open source drivers such as simonk and blheli and they are pretty popular in drone DIY world.

[kawsper]

When you mention BLHeli, don't forget BLHeli_S, and (soon) BLHeli_32 which is a re-implementation written in C (before it was assembler) built to run on 32-bit hardware (before it was 8-bit), but sadly the project is closed source :-(

[moorage]

Not more expensive than high power servo-motors! Hard to get low-RPM and position control from most drone motor controllers for robotics. I think it's mostly just different use-cases :)