Yes, there are people who play poker as a main source of income. A professional poker player could be defined as one who does exactly that. Some people make money through poker and then venture out into other areas such as business (starting or owning companies), writing (poker strategy books), etc.
The cardrooms take less than 5%, $1 for every $20, with a maximum of $3, which means the house take is always under 5%. Commercial statistics programs that track a player's own results commonly show the number of winning players between 30 and 40%, but that data will always skew since the results will almost always be from a winning player (devoted enough to keep personal stats, for example.) I don't think the article can or should tread in this territory since it can vary a lot between cardrooms, types of games (Omaha versus Holdem), etc.
Are there people for which playing poker is the main source of income?
