It is testable. Costly to test, but testable. If someone wants to test it, they could make a new account, and use it to post lots of useless insight-free twaddle, and see how much karma they get on that account. However, probably the costs of that experiment would be to high to actually pull it off. (Both the cost in time to the tester, and the cost to the signal/noise ratio of Less Wrong of adding that many more posts of useless insight-free twaddle.)