I think the answer to this, like many other things is maketing and huge mark-ups.
For example:
Why can online sellers knock-out Shimano Deore XT chainsets month after month for £105 and still make a profit (RRP £199)
Wiggle are selling a Focus TT bike for £999 (RRP £1600)
Check out FSA carbon chainsets on
CRC a while back for £60 (RRP £400)
TT/Tri aero bars - 2 short tubes of metal Alu and a couple of clamps £100 minimum - WTF!
Actually £100 for a turbo seems quite reasonable - not sure about the £400 ones though.
Got my Elite 2 years ago for £55