Have you read any of the comments in this thread? We are talking about take-home tasks that take 5 to 10 hours or more, not fizzbuzz.

You are naive if you think you solved cheating by checking technical skills on the onsite. What if I'm a 7/10 candidate, and someone else is a 9/10, but I cheat and submit the solution of my friend who is a 10/10. I'll get the flight ticket to the onsite, the better qualified guy will not, and you will have to choose from a smaller pool of candidates, in which I might be the best one.