Let me make an analogy between a multiplayer game and a night club. A night club needs a critical mass of people to be profitable. If the number of people dips below a certain level, then the club is doomed - fewer and fewer people will show up every night, until the club is empty. Thus kicking loud and obnoxious patrons is a sensible decision, because even though they are bringing some profit to the club, they drive other customers out. Which brings me back to the reason why it makes sense to kick cheaters out of the game. The presence of even a few cheaters has a large psychological effect on the rest of the players - when you get killed in shooter repeatedly by the same one or two players, you start thinking: "Is that guy cheating? Why am I getting my ass kicked?". And thus, instead of having fun, players are getting frustrated. Furthermore, I think a lot of cheaters are really obnoxious assholes. They love bragging about it, they often derive fun from making other people angry. They will belittle others for making a big deal of their cheating. In short, they're the kind of players nobody wants to play against. And just like the obnoxious patrons in a night club, they will make players leave for greener pastures, and once everyone is gone, they will go somewhere else - and do the same thing all over again.
So what all of this - which I am not pretending to be anything other than my opinion - has to do with lost sales? I will agree it may not matter so much for a game which strongest component is its single player campaign. For a purely multiplayer game though, I think it will hurt the community growth, cause it to never grow to its full potential and shrink to the state where "nobody plays because nobody plays" sooner. In the old days when all the money derived from the game was made on its initial purchase, it didn't matter so much, but as many other posters have mentioned, it will probably have an impact on games that depend on subscriptions on monthly transactions - and lo and behold - this is probably the reason your hear more of these types of stories. Companies are taking notice that cheaters are bad for them, and taking actions to attempt to fix the issue.