If the drivers were open source, they would need good programmers to maintain them. And if they had good programmers, they could have reverse-engineered proprietary drivers. But I guess that buying an old PC might be cheaper than hiring a good programmer.
It's more that buying old PCs is safer than trying to reverse engineer drivers. Buying enough extra hardware to have spare parts for the life of the product is a pretty well known and cheap way to insure no down time.
I have experienced even when the original driver writer (me) is still on staff, it can be less expensive to just keep buying old-spec PCs than rewrite the code for a new OS. I make the company more money writing new code than supporting code that's a decade old.
