Bob, I am not making a judgement here, just asking two questions.
If you receive "good" service in a restaurant, do you tip your server 2%? If you barber charges $15 for a haircut, do you tip him 30 cents?
This is a sensitive topic that creates firestorms on every bulletin board that touches on the subject. Search almost any poker site and you will see volumes written on this subject.
The bottom line is that in any service industry, you should tip based upon the service you receive. It is hard to put a % on it. Make no mistake, poker dealers are providing a service.

I once had a player ask me to chop a $1 chip so that he could tip the waitress 50 cents for bringing him a bottle of water. I was dealing a NL game at the time and did not have silver in my rack. I was not able to accomodate him, so when the waitress brought his water, he asked her to give him 50 cents change. She did. He then told her that it was hard for him to justify giving more than 50 cents for a bottle of water. Flawed reasoning in my opinion. The bottle of water cost him the same as a top shelf liquor would have cost him. NADA. Did the fact that he ordered water mean that the waitress did any less work? Nope. Did the water weigh less on her tray than a mixed drink? Nope. Maybe it is just me, but I don't get that line of reasoning.