For all that we’re liable to be on the receiving end, writers aren’t always the nicest about pointing out other people’s plot holes. In reality, writers can be really harsh critics (kind of like how teachers are generally awful students, and doctors make bad patients). Since writers know more about writing (we assume), they can find more flaws.
Of course, a little empathy and kindness never hurts when talking about other people’s works. We all make mistakes, and the harsher you are on others, the more eager they’re going to be about pointing out your mistakes.
Then again, Terry Pratchett generally had something witty to say when someone pointed out flaws in his works, too: “There are no inconsistencies in the Discworld books; ocassionally, however, there are alternate pasts.”