You said "months to learn OpenGL, then a year to code it... or maybe longer", which I think is an exaggeration, especially if we assume that any graphics programmer worth his pay is already familiar with API's other than DirectX.
The 'year to code it' was static between the two. And you're making the assumption that the dev is already familiar with with OpenGL, I'm making the -- I thought clearly stated -- assumption that he was not.
To rephrase my statement for greater clarity:
In addition to a year's 'base' time to produce the game, learning OpenGL would require learning the new API -- depending on the dev, this could take 6-8 weeks to become fully conversant with the technology, and may also impose additional development time when they run into 'easy' problems to solve using directX which now require them to come up with new solutions.
It's also not an apples-to-apples comparison, because DirectX does more than just graphics; it also helps with audio, input, and more.