Ok on the case of Fallout 3, I'd almost agree with this but here look at the maths based on the prices from my work at HMV:

Release price on 360 console: £44.99
Current price on 360 console: £19.99 in a two for £30.00 offer
Cost of each dlc package on 360 in points: 800 points each pack
Total cost of DLC packages (operation anchorage, the pitt, broken steel, point lookout and mothership zeta) in points: 4000 points
Cost of each microsoft xbl point: 500 for £4.75 I make that 105 points per £1.00 but with rounding we could say 500 points is £5 so 1 point a penny.
Cost of each package: £8.00 rounded though closer to £7.50 without the rounding
Total cost of dlc in £ sterling: £40.00 rounded, £35.00 or thereabouts not rounded.

Looking at that maths it does seem terribly expensive however consider this: Fallout 3 GOTY edition comes with a second disc containing all DLC £34.99

So if you're that deeply unhappy with the cost of the DLC buy or trade in towards a copy of the GOTY edition which comes with all of the DLC and the main game disc for essentially free with it. If you know someone interested in the Fallout 3 game without it convince them to buy the GOTY edition because you can just borrow their DLC installation disc and it'll work I know, I done it :P