[WhiteWolf]

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Thats all fair enough.. but now here is the idea. If i now take that ~$190 and stick it on a bet of ~50/50, say red or black in roulette i get the following:

EV is:

(($190 * 2) * ~0.5) - ($100 * ~0.5) = + $140



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In the first term, you use your gross winnings (190 * 2) when you should be using your net winnings (190 * 2, minus your original stake of 100). The corrected equation should be:

((190 * 2 - 100) * ~0.5) - (100 * ~0.5) = 90,

which is exactly your EV if you just take the bonus and pass on your hypothetical even-money bet. Since your actual odds of winning the bet is less than even-money, your real EV will be less than 90, and the bet will be a bad proposition.