>>happyt+E3
"Why" is redundant. If the article is stating premise "X" and it's on the front page (assuming it's not newsworthy enough that "X" is novel and worth discussion), it's obviously going to explain "Why X" and "X" is sufficient.
>>mmastr+e7
Lots of posts on HN state the fact "X" is happening and are searching for help to find the reason or just conveying a story. "Why" in the title tells people the author knows the reason and is going to explain it in the post.