Poker is gambling, but comparing to a slot machine is a little off the mark.

How many people do you know that are consistantly profitable on slot machines? How many do you know that are 40% profitable on slot machines?

Lets say one day you play slots for 8 hours and never win a penny. Then, the next day you play poker for 8 hours and never win a penny. Which day do you think you would have lost more money?

Saying poker is like a slot machine is something that people tell themselves when they've lost too much.