it's cheaper to manufacture. The matte (non-shiny) finish is another coating that requires more powerful backlighting for the LCD.
It's great if you use your laptop exclusively in a completely dark situation, but try using it outdoors, it's completely useless (I usually use my laptop as a preview screen for my digital camera for my client to see the results instantly).
The problem now is that I no longer want to lug my 17" widescreen and 15.4" widescreen laptops anymore. I want to get something like 10" or 12" widescreen, but unless I'm willing to spend close to $3K, I can't find one without that godawful shiny screen.
Even the newer Apple notebooks uses that awful screen.