There are always exceptions. Plus:
Windows CE (Which was barely used for game production on the system mind you) is in support of my argument because that was one of MS's initial efforts. They even approached Sony for the PS2 and were rejected and thats one of the reasonts they made the XBOX. The DC went for Power VR since they didnt have the funds, and yet that was still a state of the art custom hardware. Power VR doesnt exist in either PC or console space.
And how these are relevant in the console and PC gaming space?
1) I think if you look from the past forward they aren't exceptions they are a continued build up to the point we are at today. Companies always want to maximize profits and for 3rd parties the easiest way is to release on as many platforms as possible. This was true in the past and is true now. The difference is that the big players are now all using the same few companies for hardware which makes it even easier to port it to everything
2) Apple has one of the largest gaming platforms in the world. Why would it not be relevant ? Companies who supplied hardware to apple would still need software teams to ensue it works and those teams can create software for any platform.
3) Sega had two boxes in the running. An american version with 3dfx and the Japanese version with power vr. Those prototypes were dural and black belt. Sega even bought 16% of 3dfx in 1997 because of this. Ultimately 3DFX sued Sega and NEC due to them doing a back-room deal and it was settled out of court with 3dFX getting 10.5m. There is speculation that EA who also invested in 3dfx at the time was not pleased and its why dreamcast got no ea support. Even before the dreamcast prototypes there were saturn 2 prototypes using Real3d chipsets.
In the mid 1990s what did Lockhead Martian , 3dfx and video logic all have in common ? They all made pc graphics boards. So right there you can see sega as early as 1995 and the Lockheed Martin talks were already starting to move to the model that Microsoft and later Sony would adopt which is to make miniature pcs.
Heck we can add nvidia in there with the NV1 which was based off the saturn and even got saturn ports if you want to go console - pc for hardware.
But lets not forget Nintendo who released the gamecube using an IBM Power PC cpu and an ATI / Art-X gpu.
In that generation of machines which is the dreamcast , gamecube , playstation 2 and xbox only the playstation 2 used its own custom hardware for both gpu and cpu. The dreamcast of course used an updated version of the SH line of chips with the sh-2 in the saturn and sh- 4 in the dreamcast.
In the next generation sony would use custom power pc chip design in cell but an nvidia gpu.
The take away is that almost over night from the release of the first 3d accelerators on the pc , the consoles jumped onto the band wagon. Which made quick ports much easier. This wasn't microsofts doing. It was technology changin. Fast forward 20+ years later and with only two major players and a tightly controlled api in Direct X the two players are making similar enough hardware that its never been easier to make ports.