<<
There is a case that borders on this. Namely, the DR-DOS. Basically, DR-DOS was a competitor to MS-DOS. DR-DOS was superior in many ways to MS-DOS, and it had things like disk-compressor and memory-manager (you know, to maximise the amount of free base RAM) years before MS-DOS got 'em. In order to harm DR-DOS, MS deliberatly Modified Windows 3.1 in such way that it checked what version of DOS it was running on. If it was DR-DOS, it would display error-messages. The truth was that there was no reason why Windows wouldn't run on DR-DOS, MS just made sure that it wouldn't Caldera then sued MS over that issue, and MS settled out of court. >>
Actually, CP/M (control program / monitor) was written by Digital Research Inc (DRI). Microsoft DOS was basically a clone of DRI's CP/M version 1.4(86), but further modified and called QDOS by a man named Tim Paterson of Seattle Computer Products, was then purchased by Microsoft and then licensed to IBM. To keep DRI quiet about this, Microsoft claimed it would offer CP/M-86(the basis of MS-DOS) as an alternative to MS-DOS with IBM. However Microsoft charged almost 6 times as much for DRI's version.
This is when DRI went back to work and released DR-DOS, which as you said, was very superior to MS-DOS because of all the reasons you listed. This forced microsoft to alter it's pricing for DOS, and to also release versions 4,5,6 of DOS to try and catch up to DR-DOS. What you said about 3.1 checking for DOS versions is probably true, though I cannot confirm this information. It would make sense, since Caldera, which bought the rights to Novell's ownership of DRI, sued MS over this and I think they won.