The term free blackjack has a few different meanings when it comes to online casinos. Some "free" sites allow their users to play blackjack for no money--hence "free." This is usually an inducement for fence-sitters to come on down and choose to play. After all, there's no money at stake. At least, not initially.
Of course, many of these players then have a modicum of success and figure their strategy must be foolproof. They then decide to invest a modest sum--say, 20 dollars--via credit card deposit to see if their lucky streak will continue. This is usually the first sign of an online gambling addict in the making. At this point, most online casinos have done their job.
Other Types of Free Blackjack
Other casino gambling sites advertise free blackjack in the form of bonuses. Sign up by placing a 100-dollar deposit and you receive 50 bonus dollars to play with. The average casino can afford to part with this money since it will only win it back in the long haul. As you may have noticed on your last trip to Vegas or Atlantic City, there aren't that many casinos going out of business.
In spite of this fact, most gamblers still believe that they're immune to the laws of basic statistical probability. Hence, there are increasing numbers of users signing up for free blackjack everyday. Online gaming offers all the same high-stakes action as live casino gambling, without the gas, hotel reservations, and all-you-can-eat buffets. As you might imagine, this can be a very persuasive sales pitch.