Opinions differ on the anti-trust thing... Personally, I don't understand it. I don't think anybody was forced to sign the contract.
If the democratic will of the People is that the government regulates business that's one thing, but retrospective laws are just insidious. A level playing field up front is the only fair way.
Unfortunately there's no bright-line rule that lets you know that today, you're a monopoly. You might write such a sales contract legally on Monday, and on Wednesday cross the invisible antitrust line which (after years of later largely subjective legal argument) obligated you to stop doing the same things that led to your success. So signing the exact same contract Friday would be illegal.
Not quite the same thing IMHO. By not signing the contract and doing what Microsoft wanted, since it was the de-facto standard at the time, you were pretty much kissing your PC sales business goodbye..
Look, anyone can make the offer MS made. If they price it low enough, they could get some takers. It was a smart move, because it meant that a dominant player would have growing market share among manufacturers who worked with them, but it would only work out if the product had traction -- otherwise, dealing with MS would just be paying Bill Gates to watch you fail.
"Hey... Your competitor just signed this deal that allows them to include our OS for pennies. I see you will have a tough time competing with them unless you sign it too".