You should see some of the tilted tires I see going down the road. Never ceases to amaze me what people do to their cars to make em ride like they do. I also have that slight tilt, both sides, and the tires are wearing even as well. Maybe the inside sidewall flexes just a little bit more than the outside sidewall? Car track straight, no uneven wear, not a rough ride (especially given the tires are 7 or 8 years old now) so I wouldn't worry about it if the tires aren't wearing abnormally.