it's been my experience that the ambient lighting dictates what works best for you. High ambient light does better with matte finish because the screen isn't reflecting all that light coming in from behind you. I was working on an imac in a breakfast nook and had to close the drapes on the patio because all I could see on the screen was their pool. My MBP is a matte screen for similar reasons, I use it outside too much. matte screens do tend to 'soften' the image just a little bit, removing a tad bit of the sharpness.
Graphics artists tend to work in low lighting, and are interested in very deep blacks and very sharp images, and glass gives that better than matte. LCD itself isn't exactly ideal for really deep blacks either, but LCD screen tech has come a long ways.
