After I noticed that straight vertical surface on few cars I started real-life observation and these style of wheel arches is actually on nearly every modern car:
http://www.ford.pl/spg/getImage.asp?...l_LC_13860.jpg
And that's on a pick-up!
And here - an older vehicle - curvy all the way:
http://www.mycompactpickup.com/inclu...ckup/truck.jpg
And an image of my production - it's awful, but I hope it explains something:
After looking at my own picture I think there is sth to do with wide tires better fitting in the new design, but it also reduces the space between the wheel and the fender.