Assume you've got a a super-successful app making $100k/month. Then a bug in the market messes up its ratings (like it did last Friday) and as a result they lose ranking and several hundreds of thousands of dollars over the next few months. They complain about it in a forum, and a helpful engineer says, "Oh, yes, that's a mistake we pushed to the Market. Sorry our testing procedures aren't better. I'll fix it right away!"
Bang, they've just publicly admitted negligence, and that developer could sue them for the lost $$$.
Again, I have seen NO proof of this. It's a going theory primarily because the money-oriented arms of Google (Market, AdMob, AdSense) are also the three that are the most tight-lipped over support issues.
But certainly it becomes much easier if you have evidence from someone inside the company.
YOU don't really need to see how they could be sued, or how an engineer's comments could put them at risk, in any event. If Google's legal counsel believes it to be a risk, then that COULD be what's going on behind the scenes.
And this is exactly the kind of thing that a lawyer would advise, which is really my only point.
There are a number of Google Android developers who post to the various lists on a regular basis, answering tons of questions and quickly promising to fix bugs when they're identified.
There's a going theory that, because the Market involves money (like AdMob), the developers are under gag order from Google to not say anything, and all communications that do come out are filtered through legal.
I'm not justifying that as a practice, but just putting it out there that it might NOT be the fault of a reticent (or incompetent) Market team.
Though given the number of Friday-night releases that break things over the weekend (like a recent "oops! lost half your reviews!" bug), the incompetence theory has a lot of advocates.