My guess: the leagues we're in are more beginners leagues... not that I say that we are (well, not all of us), but I guess 40% agression works fine, unless your opponent plays 70%. If you're playing cup matches, champions league and so on, you need the health more, so you have to play with a lower agression. But this goes for your opponent as well.
I played last match on 50% and I won. The match before was on 40%, and I lost... but that was v.s. the number 1. I think I can afford to play 40% v.s. the bottom half.
Oh, if only this was hattrick, then these statistics might be publicly available...