>Maybe some selection bias is going on?

I think the selection bias is 1980s companies because that was the context. (Linux is 1991, Java 1995, Google 1998, etc)

From the 1980s, the major software companies that's still alive today, you have:

  Intuit (Quicken/TurboTax), 
  Adobe, 
  Computer Associates, 
  Autodesk

Intuit was one of the few that survived direct Microsoft competition from MS Money and MS TaxSaver.

Adobe and Autodesk survived because Microsoft never entered the professional graphics editing market of Photoshop and CAD drafting. If Microsoft did try to compete, they still might have lost to Adobe and Autodesk but it sure helps when Microsoft ignores that market. (Microsoft sort of had a competing edocument standard of XPS to Adobe's PDF but that initiative didn't seem to have all of MS's attention behind it.)

Computer Associates (now CA Technologies) was this weird corporation that basically did a bunch of acquisitions of forgettable companies. I can't think of an instance where CA and Microsoft competed head-to-head. CA bought a database programming 4GL (Nantucket Clipper) in 1992 but the DOS based programming languages were already starting to die by then so MS Visual Basic for Windows didn't really compete fiercely with it.