The thing is, how can we know you're telling the truth? Someone I used to play with would afk in the middle of games all because his/our team was losing and he was calling bad plays we weren't willing to do. IE; trying to contest baron when 3 of us our dead and the entire enemy team is there.
He would sit in fountain afk and only rejoin when he got the afk warning, then claim the client crashed. The only reason I found out he was lying is because he tried to pull the same stunt while in a Skype call with me, and I could hear League coming through HIS SIDE of the call.
Just because you say the client crashed, didn't mean it really did. Sure, it could have, but how could we know?
As such, it IS fair to report for someone leaving games, even if it's just because "the client crashed" since we have no way to know and it's not hard to lie with text.