Let's cut out the bit about duplicate IPs. This has never been, and is not, a reliable indicator of anything on its own. However, in tandem with other identifiers, this could be considered as a factor.
The plain fact here is that, clearly stated in the terms and conditions, only one account per computer will be allowed, if I am not mistaken. This itself is reason enough for a casino to close an account.
Also, same country/town can be safely ignored as you have already identified that it is the same computer.
Same game is not a reasonable method of detecting anything other than a liking for the same game and must be discarded.
Same bonus coupon - well, I think if what Fuglac says is true, and that it is the same coupon for new signups, then this can also be discarded.
Same bank - how about same account? We can't ban all players who have accounts at Bank of America, now, can we? This can be discarded.
Same play and wagering style - this would depend much on exactly what style we're talking about. If the player had a habit of betting $1 each hand, that would pretty much match up with every grandmother I have ever seen play blackjack
And if both knew basic strategy, you could hardly call that a factor in identifying bonus abuse.
So only one significant factor - same computer - and as this is clearly stated in advance, you cannot expect the casino to make an exception just for you, even if you are a legitimate new player. You also cannot expect to break the law anywhere and then ask them to make an exception for you because you are not a local and don't know the local laws. That sucks too. But that's life.