You mention that: "in GEM, a portable graphical environment which would undoubtedly have brought the GUI to the low-cost PC desktop years before Microsoft's Windows"
It is unfortunate that you forget the past. GEM "did" bring the GUI to the low-cost PC desktop. But, you might say that Apple gave the "coup de grace" to DRI with their GEM Lawsuit. DRI was forced to change GEM significantly and pay lawyers fees to Apple. GEM was never the same after that and even worse, Apple's victory took much of the market from under the GEM system and DRI. Blame Apple. Not to hail Microsoft, but once they had the money for the lawyers, they were the only ones that took Apple all the way to the U.S. Supreme Court and won (except for the garbage can). It was not IBM nor anyone else, it was Microsoft; and a monster was born. You might say that the field had been weakened (all other predators eliminated) by Apple and once they were out of the "picture" (sorry for the GUI pun) the MicroSoft infectious disease took advantage of the situation and devoured the host (we).