Ignorant question time. Do all push bikes with disk brakes have fluid operation
all the good systems do
lets put it into perspective about 8-10 years ago when i begun getting seriously into mountain biking (let it slip recently if im honest) a cable disc brake cost in the region of £100 (caliper, pads and disc) then you had to add on the cost of the lever and cables and outer hose (cheap cables were no good as there was too much stretch and the cheep outer suffered with compression in the wire wrapping leading to spongy brakes )
anyhow the same brake can be had for £60 now
http://www.chainreactioncycles.com/Models.aspx?ModelID=31347
but they need regular stripping and cleaning as the cable is exposed at the actuator lever (yellow line in pic)
so each time you brake even though there is a little rubber seal water and grit get drawn in and migrate through the outer hose increasing friction leaving a crap feeling in the brakes...
and they have to be manually adjusted (constantly on a really wet gritty ride)
but they are simple to work on...
the Hydro systems its obviously sealed so muck can't get in the pads/ piston self adjust to wear and they have a consistent feel (unless you manage to find somewhere with the Mother of all hills and manage to heat the brakes up so much you boil the brake fluid

then the lever comes back the the bars and have no power

but smart use of the brakes helps
(then again these brakes that i boiled have the older stainless steel pistons newer ones have "phelonic" pistons think bakealite heat proof plastic which isn't conductive so the heat stays away from the fluid reduceing the chances of boiling...)
both systems can suffer from brake fade the same as a car
nope
ours will be cables since we are cheap and dont need hydralic
what bike you looking at buying daz? if you just want a round town and odd jaunt in the forest look for a bike with V-brakes not as snazzy but they will work..... pads/blocks are much cheaper and easier to get hold of (try finding pads to fit on some of the unbranded made in China disc brakes)
same can be said of suspension forks decent ones (ones that actually work and don't behave like a pogo stick) cost upwards of £200 so what quality are they going to be on a halfords £120 special baring in mind you still have to fund the rest of the bike so you get a crap chain, gear system etc as they have to fit the Forks/disc brakes into that price point .....
in a nut shell you get what you pay for
if i had the option between these
£190 full suspension with disc brakes:
http://www.halfords.com/webapp/wcs/..._productId_253075_langId_-1_categoryId_165499
and this one £180 Full rigid
http://www.halfords.com/webapp/wcs/..._productId_253053_langId_-1_categoryId_165534
i know which i would choose if i was after a "reliable" bike and one thats cheaper to keep going..... Try and source a rear Bush/ bearing for a cheap suspension bike pivot

bad enough getting hold of them for a £2k bike (cost me £20 each last time and i needed 4)