With the production lines that these manufacturers run, yes it is more expensive for them to pull a subset of computers and not load their bloatware windows image. That just isn't a situation they are setup for. You can argue about whether or not it should be this way, but that is the reality of the computer manufacturing process. Sure, it's more accurate to say they won't do it, but in all likelihood, they can't do it and keep their profit margin.

Now if they were to stay that they were contractually obligated to install windows on every machine, then they'd have a problem.