While your point is valid, there were differences in some things such as how IBM handled their anti-trust case compared to MS. IBM had a consent agreement with the DOJ and mostly followed it with one result the rise of MS, which at least partially due to IBM's consent agreement got a very good deal on DOS, along with a more open philosophy from IBM. Compare to MS who immediately tried to work around their anti-trust agreement and got political resulting in Bush basically cancelling their anti-trust case.
A good example was the competing operating systems on the PC in the mid 90's.
You had OS/2 (v2+) which during install, if another OS was on the system, installed a Boot manager, called BootManager, which upon boot allowed you to multi-boot, DOS, Windows, OS/2, Linux etc. Meanwhile with MS, it monopolized your HD. Install Win9x on your multi-booting HD and at the end of the install, it would inform you that it had wiped your OS/2 install. No warning, no mention of how a minute or 2 with fdisk could return your multi-boot environment. Imagine, you test a new OS and after installing it, you are informed all your stuff is permanently gone, even though it actually was still there.
Another thing with installing Win9x was that if you had OS/2 installed, it didn't worry about if you had a serial number to enter during install. This continued their attitude that a pirated version of Windows was better then a paid for competitors OS.
OS/2 also mostly followed standards rather then creating their own like MS.