Ha, rather interesting, I'm kinda doing the exact opposite.
I'm building my engine in DX9 because I find it much easier for some reason, then once everything's working and I've started producing games with it, if I'm popular enough I want to transfer the engine over to OpenGL for it's portability.
Pretty much all of my engine is completely portable apart from the graphics, and a special launcher I've developed for Windows. Once the engine is running on OpenGL I'll only need to create 2 more tiny launchers and then any games previously written in OpenGL for windows (between the times of developing the engine for OpenGL and developing the new launchers) will be able to be thrown on Linux and Macintosh with hopefully no problems
By the way you'll shortly realize how dumb of an idea going WinAPI is.
It's so cool as you have more features.
But will your program act correctly on a different Windows version?
Will your program be compatible with the still-in-use Windows XP?
How much time will it take for you to "convert" your program to be compatible with other systems?
If you're going to get a job, that's something you have to take in mind.
You cannot just assume.