But when you subdivide the cube, those edges don't STAY sharp. A edge that stays sharp, even when subdivided, is called "Creased", maybe I should have been clearer. :)

Here's a example:

The top cube has been subdivided 3 times, and now looks like a sphere.

The right cube has 2 edges creased, these edges stay sharp even as we subdivide.

The left bottom cube has 2 edges with a slight bevel. These stay somewhat creased as the cube is subdivided. It depends on how close I can make the 2 edges when beveling. The closer they are, the more it will be creased. If you add a 3rd edge between the 2, it stays even sharper when subdivided.

Ideally, collada (which supports creased edges ) export and X3d would be nice too.