I think the point is if everyone had an economy rate of 4.86 average score against would be 243, which is a decent total, but if Anderson is the most expensive then the score would be 220-230 or maybe even less, which you would hope the batsmen could score.
Also if he opens and bowls at the death there is the issue of the fielding restrictions, and if he takes a couple of top order wickets maybe that is why other bowlers have a better economy rate, etc.
Brett Lee's economy is 4.69 and he has played 73 ODIs, plus he manages to get a regular gig in the best side in the world, so economy rate isn't everything.
Shoaib Akhtar, 87 games, 4.56.
Waqar Younis, 262 games, 4.68.
Jacques Kallis, 180 games, 4.70.
Zaheer Khan, 70 games, 4.63.
As you can see there are several top world bowlers who have economy rates over 4.5.