Why are these things do damned expensive in retail and oftain online?

I can get a simple two part VESA 100 LCD bracket online in a few places for about £5, yet all the highstreet chains and computer places are about 4 times that for exactly the same thing.

I would very hapily pay £10 for the convenience of buying it tomorrow instead of messing around with deliveries for such a basic part. But no way am I paying £20.

Here is an example:
Omnimount Fixed LCD at PC World - Buy cheap Wall Bracket - Omnimount Fixed LCD Small Fixed Mount for 13 - 24'' Flat Panel TV's
Omnimount Fixed LCD Wall Bracket - £19.99 (plus £4.95 delivery if you so choose)

Small Wall Mount Slide Bracketrubbish::rubbishLCD / Plasma TV Supportsrubbish::rubbishCable Universe
Small Wall Mount Slide Bracket - £5.45 and postage is about £3

Crazy I tell you, just crazy!