Here's a great example of using a corporate blog to explain an unfortunate product decision to customers, "Living Photoshop: Macintosh and the Intel switch".
The blogger Scott Byer explaining why Adobe isn't going to release a MacIntel version of CS2: the summary being that transitioning their entire development over to XCode wasn't feasible for CS2. It's what Adobe's Mac customers need to hear (that there are significant technical hurdles which didn't make sense for a product currently in the market) but it's not the kind of thing that a press release can explain. In other words, it's important information, but without bloggers, there's no clear channel for how to communicate this stuff.
It's also of note that the comments list (the conversation) stretches far beyond the length of the original post. The customer feedback is mixed -- ranging from "You guys suck, I spent $1000 on this software!", to "Yeah, I understand the challenge first hand. Thanks for the explanation."