In addition to consideration, prize and chance are the other two elements of gambling.
1) Consideration usually means players must surrender something of value to be eligible to participate.
2) Prize includes not only money, but anything of value.
3) Chance means the outcome is not determined by skill.
In your example, tony, there is obviously a prize and card games are largely determined by the luck of the draw (legal jurisdictions legislate what is considered skill), but there is no consideration "no purchase necessary". I'd say it's not gambling -- more like a free raffle. There's no chance of any participant losing anything.
Here, if there's nothing in it for the police, forget about it.
