The point is that Many people already have the directX 9 drivers installed, and that they are a lot less likely to NEED to latest videocard drivers with DirectX simply because historically video card makers have given significantly better treatment to DirectX support than openGL support.
If they've got DX9 drivers installed for their card they've already got OpenGL support unless they've got a low-end Intel or SIS card more than three years old. The problem is the people who don't have recent drivers, who only have the version of DX (7 or 8) that's bundled with Windows, and have the same drivers they bought with their PC a couple of years ago.
My own laptop for example, I'm looking at a difference of several hundred FPS for directX, and 5-8 FPS for a similar program using OpenGL.
What laptop, what video card, and what application?