Well, the scam is definitely going to work on those "greedy" gamblers. When they see a huge amount on their account that they won by just depositing only $5, they might be tempted to actually deposit the $100 the casino is requesting, just to try their luck, and that's exactly how this scammer is going to keep spreading his link, hoping that someone like that clicks on it.
But, as far as bitcointalk community is involved, all those who actually "read" the post aren't going to fall for it.
Yeah, a 100$ may be a big money and some of the people wouldn't deposit that money and move away but what if they would have asked for 5$ or 10$ deposit, in that case, even a person who knows its an obvious scam, would have deposit that little amount thnking what if it is real and even in case of scam, he will only lose little amount.
This is the mentality that is usually engineered for most scams, and I have seen such online services that ask for a little deposit in order to get a bigger withdrawal, all of them are running because of the people's greed

In fact, there can be some people who fall into something like this because of the big money won from the free balance.
The reason is simple, most people want money and if there is something like "deposit $100 to withdraw your $50k-$100k" then I believe some people will try to gamble by making deposit.
At this stage, some people may think "ah why not risking $100 to withdraw $50k-$100k or even less like few thousand of dollar?
This is why in this casino, they give free money for new players then give easy big win in order to run the scam scheme, later once the users win big and want to withdraw then they will ask users to deposit first.