I've seen discussions of this for years on different boards. I've noticed that few people have seen serious problems such as tires blowing off, so I think the LBSs won't get much extra repair traffic based on a tire-rim width mismatch. From their point of view, it's not a problem, the wheels are still round, rolling, and black. But if you value quick wheel removal, or extra security, or lack of squirminess in your wheels, it's probably best to select rims/tires along the lines of that chart given earlier in this thread.