Exactly. If it was libellous, then DO do need to protect themselves. However I felt that blog post was genuine, on first impression of reading it, and I think there was enough evidence that it may actually be true that DO should not have been anywhere near as quick to take it down, perhaps they should have investigated it more.

That is, if the reason for taking it down was entirely to protect themselves legally. From what I've read, it's hinted that this might not be to protect themselves, but might be more down to them just wanting it gone.