Im always getting the dreaded message: Oops We are sorry, the URL you have entered cannot be displayed On almost every link going to yahoo answers from google. This is stupid, and if yahoo are just going to randomly delete questions off their site the least they could do would be to link to a similar question, instead of throwing up the same vague generic error page.
There's lots of crap and spam on Yahoo answers and most of it gets removed, but Google needs sometime to remove those pages from their index.
I don't know what you are searching for, but I am not able to replicate the problem. I suppose the things you are searching for are from deleted Qs in YA, and not Qs that are still live on te site. But I agree with you. From a business and marketing standpoint, it is fascinating that Yahoo will not take advantage of this traffic. I wonder if their web analytics team have actually studied how much traffic their Opps Page Not Found is getting that is coming from the search engine