it isn't a matter of whether the game is a sport or not. It is a game. To some, it is a sport. "sport" cannot be defined properly here. Simply because it is all how it is percieved. A lame example: to a hair stylist, clipping is a sport.
And as someone mentioned previously, luck IS involved. It is hard to deny it. But poker also has other variables involved. Such as, skill (how well you hide your expressions and tells, making good moves, reading other players), WHO is playing, the number of people playing, your chipstack at any give time...there is countrless variables which can determine who wins the game. The same can be said of many sports.
All I'm saying is, Poker is a sport to some people.