You hear that kind of excuse a lot, just like when a politician does something particularly egregious (e.g. Obama's FISA vote) you hear people explaining, "Oh, that's just a compromise to get more votes. He can't do anything if he isn't elected."
The problem with the stock explanation is that it's very often just wrong. Ebay's current emphasis on big sellers at the expense of individuals is losing them money, just like Obama's FISA sellout is losing him votes. Piss off your core market to chase some other potential market, and odds are you won't do well with either. By all means, businesses should try to expand their customer base and politicians should try to appeal to more voters. But when you abandon the people who got you where you are in the first place, you're almost guaranteed to suffer overall.
Businesses that do well are those which build a steady, loyal customer base that keeps coming back for more. This is particularly true in the online world, where changing to a competitor is very, very easy; the few success stories to come out of the dot-com mania of a decade ago show how to do it right. Amazon, for all its evil, still does a damned good job of selling books. Google, no matter what else it does, remains far and away the best general-purpose search engine. Until a couple of years ago, I'd have counted Ebay among those success stories, but now it looks as though they were just as flaky as any HowFastCanWeBurnVentureCapital.com site; they just took longer to show it.
Suits and their sycophants love to talk tough about how they serve the bottom line ... but in the real world, the suits are wrong more often than not, and here's a sterling example.