I figured that EGA was very rare as a stock-option in clone PCs (it seems that quite a few of them used an ATi Graphics Solution/Small Wonder), so most EGA cards out there would have been original IBM cards in original IBM PCs.
There was only a small window of opportunity for upgrading a CGA/MDA/Hercules machine to EGA, because VGA arrived on the scene only shortly after third-party EGA cards did, so in my experience, EGA aftermarket was never big.
Then again, as I say, it could be a geographical thing. In my part of the world, PC gaming didn't take off until the early 90s anyway (386SX-16 with Trident VGA seemed to be an early 'standard', around the time that Wolfenstein 3D became popular). So there weren't many people who had a PC at home, let alone that they were interested in upgrading the graphics capabilities.
You are correct, for several reasons.
One, the IBM PC was released in 1981, but that was in the States, and by the time they had sorted everything out with a supply chain to Europe and different power supplies, etc, 1983 had rolled around, so the PC market in Europe only really started two years late. The EGA card came out the next year, too soon for Europeans to upgrade their only-just-purchased MDA/Hercules/CGA PCs and clones.
Two, IBM-compatibles at the time were a lot more expensive in Europe than in the US. Actually, they were also not exactly cheap in the US, but the bigger country had a bigger market of people who could afford them, and then economies of scale started to kick in.
In Europe, a lot of personal computing was still done in the realm of more affordable home computers, which is why your C64/Speccy/Amstrad/Atari ST/Amiga type of machines had much more of a run there. So the PC market also moved slower.
Even as late as the very early nineties, a full decade after the initial introduction of the IBM PC in the Land of the Free, you could still walk into a high street computer shop in Europe and purchase a new XT clone. That's at a time when the first 486 machines were hitting the market at the opposite end of the price list.
VGA came out in 1987, just as some of Europe's early (i.e. 1983+) adopters of IBM-compatible PCs were getting ready to upgrade.
Once again, you are correct. While EGA
software support was not rare, EGA
hardware was significantly rarer than CGA/Hercules or VGA. Just try and find an IBM 5153 CGA display. You'll probably find one if you're persistent. Look for a VGA monitor. No problemo. Now try and search for an IBM 5154 EGA monitor. See what I mean? Exactly. So you are entirely correct, certainly for Europe, but probably, to a lesser extent, also for the United States.
A final note on EGA software support: Note that Commander Keen was released long after the advent of VGA hardware, but it officially only required EGA. Many developers made the same choice, because apart from any technical reasons, targeting EGA was "good enough" and gave them support for two hardware generations for the price of one. Yay backwards compatibility.