If I remember right, most manufacturers get there frames from an outside vendor. These come in stacked 6 or so high and come with tires (from what I've seen). So coachmen don't have piles of tires sitting around, but a company like lippert will.
2011 Coachmen North Ridge 290RKD 5'er
2005 Dodge quad cab dually diesel 6'spd manual
1 weird cat with an occasional attitude problem.