U know I thought the same thing but look at it this way. The last couple of years Real bought kaka, Ronaldo and Benzima, and they already had Higuarin. Barca bought Villa and already have messi and some of the best attacking mid's in the world. Chelsea have drogba, Anelka and they bought Torres. Man Utd have Rooney but don't seem to be spending as much as they have. City have Tevez and bought Dzeko and Balotelli and almost every other attacking player that was available the last couple of seasons. Milan bought Ibra and have Pato. Merda have Eto, Milito and Sjnider (sorry bad smelling).
Apart from those teams who in the world could either afford or would attract Aguero??? Not too many and with the major investments those clubs have already made in the last 2 seasons, realisticly they would need to sell to fit Aguero in. But that's just my opinion.