Originally Posted by
Kimmo
No it's not; that's the point of a disc, whether it's cable or hydraulic.
er yes it is, the question was asking about disc and rim brakes, there are / have been two systems of hydraulic braking available on bikes, rim and disc, the rim system that the OP was asking about, has only been made by Magura (HS66), this is no longer manufactured, so all current hydraulic brake systems are by default disc. At no point was the question about cable operated disc bought up till you did.
The original post was specifically about dropbar brakes, as you can not get any dropbar hydraulic rim brakes, it makes your argument pointless as there are none currently commercailly available.