An "exclusive" isn't as much about it only coming out on one platform as about said platform's owner having a contract for it not to come out on other platforms. This is done for the typical "I'm going to buy console X because of game Y" sales.
The PC exclusives you're referring to aren't as much PC exclusives as simply titles too small to be able to afford the cost of entry on to the consoles. If you think about it, most games with big publishers come out on consoles as well as PC.
The reason big titles are very, very rarely PC exclusive is that it'd require someone big to pay money for the title only to come out on PC, and who's going to do that? Most people own a PC, so it's unlikely to drive PC sales, and even if it did, you can't be sure that the PCs being sold are going to be equipped with hardware/software from whoever's pushing the exclusivity deal.
The PC exclusives you're referring to aren't as much PC exclusives as simply titles too small to be able to afford the cost of entry on to the consoles. If you think about it, most games with big publishers come out on consoles as well as PC.
The reason big titles are very, very rarely PC exclusive is that it'd require someone big to pay money for the title only to come out on PC, and who's going to do that? Most people own a PC, so it's unlikely to drive PC sales, and even if it did, you can't be sure that the PCs being sold are going to be equipped with hardware/software from whoever's pushing the exclusivity deal.