If you are really in a "professional" environment, isn't it possible to put a portable computer in a more favorable position, or adjust the lighting to your needs.
No, that's not always an option...
First of all, the point of a notebook is to be able to work outside of the work place. For instance, it's becoming increasingly popular to work outside - sitting at a coffee bar for instance. There, it's kind of hard to switch off the sun, and you might not want to have to fight with the other notebook users for the few reflection-free spots...
Likewise, a very popular work place is the train (or the plane). You can't adjust the lighting, you can't shift position and the lighting will just as the train runs its course. For instance, my girlfriend sometimes spends 6 hours travelling by train during a single day. She *needs* to be able to work during her whole trip - otherwise, she will need to catch up at home, and this is not fun, or, even worse, she won't be ready for her meeting.
Notebooks are really meant for that : having a computer in working condition anywhere anytime. Having a matte screen just widens the range of situation where your notebook will be able to work as a notebook. Having a glossy screen just makes it more like a transportable iMac.
Laptops are a trade off.
Exactly. The trade off is that I will buy an expensive and limited computer for the capacity of being able to use it everywhere. The matte screen is part of the trade off : I will lose somewhat on the quality of movies (anyway, you already lose a lot by watching them on a tiny screen) for the ability to really use the laptop everywhere.
The glossy screen trend is messing up the trade off completely, by attempting to make the notebook somewhat better at something it will always be bad at anyway (watching movies on a screen too small to even benefit from HD) while making it worse at being a notebook.