My observation is that disc brakes are the new "must have" item in order to sell a bike. As a result more and more bikes that have no legitimate need for discs are showing up with discs, often making the bike worse.
Here is what Thorn (maker of high end touring bikes) says about disc brakes:
“V” brakes
Vs Hydraulic discs.
There is no doubt that hydraulic disc brakes are
preferable to V brakes in the deep, muddy
conditions often found in UK mountainbiking.
They are, however, very easily damaged
(especially in transit) and a bent rotor is much
more difficult to straighten than an “out of true”
wheel. Indeed, if the rotor is warped enough, the
wheel will not even turn! Don’t compare the 8 to
10mm thick, cast rotors, found on modern cars
and motorcycles, with the 2mm thick, stainless
steel plate, rotors found on bicycles.
For everything, apart from full-on
mountainbiking, we prefer the
simplicity, ruggedness and ease of
maintenance of V brakes. We even
prefer the “feel” of top quality V
brakes. We have rims available, with
a tungsten carbide braking surface,
which provides fantastic braking
combined with exceptional longevity
.
Please don’t ask for a
disc brake on steel forks,
we simply won’t do it!
We use raked blades, these are exceptionally
comfortable, they will withstand the forces of
cycling (and have done so for generations) but
raked forks will not withstand the forces
generated by a disc brake, which are very
different to the forces generated by V brakes,
even at the same rate of ***********. We have
seen 3 ways that other manufacturers have
“accomplished” this, they all seem stupid to us
(1) We have had customers complain that a
well known custom builder’s raked steel forks
have permanently bent under braking.
(2) We have seen hideously uncomfortable,
thick walled, straight blades used by another
manufacturer, these forks don’t fail, but I
expect that an owner’s hands and elbows
soon would!
(3) The most ridiculous “solution” of all, is a
heavy left blade and lighter right blade. The
different blades must have different elastic
properties (isn’t that supposed to be the
point?) and therefore the axle must twist, when
a bump is hit. If the axle twists, then so must
the front wheel. If the front wheel twists, then
the bike consequently alters course.
Isn’t hitting bumps comfortably and safely
the main function of a bicycle’s fork?
Why compromise comfort and safety, in
order to fit a brake, which is inferior, in the
conditions that the steel fork will be used in?