Carroll's transfer fee was inflated because of his youth, his Englishness, the fact he had recently signed a new contract, his leaving in the January transfer window, and because the type of centre forward he represents is hard to find.
If you are going to sell Torres in the January transfer window, then you have to make an emergency buy to cover the loss in the short term. Chelsea had to overpay for Torres, and Liverpool had to overpay for Torres' replacement.
I don't think it is all about Carroll's goalscoring. The advantage of a big, bruising target man like him is that it creates opportunities for a player like Suarez to play off of Carroll to get his goals. It also helps the team release the ball forward to Carroll. This sort of player is hard to find and costs plenty.
If Carroll had a year left on his contract, in the summer, and if Liverpool already were well supplied in his position, then no way Liverpool would pay that much for him. A thirsty man in the desert will pay whatever it costs for a glass of water.
United on the other hand is well-watered and therefore has the luxury of investing in the future with players like Phil Jones who may not have an immediate impact.
Downing has always seemed to lack pace for me. Or if he has pace as someone in this thread claimed, then he isn't able to use it to beat players one on one often enough. He delivers a nice cross and has goals in him, but he won't scare opponents.
Tottenham will finish ahead of Liverpool as they have blazing speed on the wings in Bale and Lennon, and they have a more balanced team which can build from the back rather than depend on Gerrard to create something from nothing.