Why does this do nothing on ATI but fine on NV?

GLfloat q = 0.9;
glAccum(GL_MULT, q);
glAccum(GL_ACCUM, 1 - q);
glAccum(GL_RETURN, 1.0);

OK Has anyone actually tried it on an ATI and worked? Here’s a very easy tutorial to try it http://tech.bombinaid.com/post.php?id=12

Accumulation buffer is not supported on most ATi cards iirc.