Look at this example: Insanity Dice has a 20% house edge so if I have 10 bitcoins I will start off with betting 2 bitcoins. The chance of losing 4 bets in a row on insanity dice is 13% so it is pretty unlikely for you to lose. If you do happen to lose you now bet 6 bitcoins and you will have a 7.7% chance of losing 5 in a row.
Any one who consider 13% or 7.7% chance of loosing as low had never gambled before

As stated already, any operator of gaming "sites" who encourages punters to bet using martingale as a "sure win" strategy is totally immoral or idiotic: since there is a clear conflict of interest here: by posting a "winning" strategy, is the "house" prepared to loose everything to players. Obviously not.