I have touched on this in another thread, but lets take O`Shea as an example, btw i have no idea how much he is actually on, but this financial fair play rule is probably the reason, and you can pay them more per week on a 4 year deal, than a 3 year deal and loose less money (according to the fair play anyway)
6 million over 3 years = 2 million per year, lets say we give him 25,000 a week.
with the fair play its 6 million over 4 years = 1.5 million per year but then you can give the player the extra 500,000 per year, so you can offer the player 35,000 per week
yes over the 4 years the club itself will be paying more, but to Uefa who only takes the last 3 years into account, you are paying exactly the same either way. but you have more chance of getting the player with the higher wage.