I'm actually surprised this hasn't happened in US more. There has to be more to that story than just retailers not wanting Ubuntu on laptops, when they could save their customers at least $100 on the machines. It's also strange that in many other countries retailers would still sell you machines with FreeDOS (to save customers money), but not with Ubuntu or other Linux distros, since FreeDOS is all but useless.
My guess is Microsoft is coercing both OEM's and retailers somehow, and if they really have to sell the machines without Windows, then they want them to at least sell them without a real OS on them, that their customers might actually begin to use as it is.