As for the calls to "change something", if he's cheating then limiting the maximum bet won't stop him winning, and if he isn't cheating and is just lucky then limiting the maximum bet will only slow his inevitable losses. I don't see how it helps in either case.
I disagree with dooglus on this point. Now the investors are in the situation they cannot understand if nakowa is cheating or not, because with large bets what happened in these days is still somehow plausible. Indeed, if you run some simulations as elm did 242962.msg3222672#msg3222672date=1379981987 you can see that few times nakowa is winning. However if you run the same simulations with a much smaller max bet, like 0.01% or so, but the same amount of wagered money, you may check that the same behavior is ridiculously improbable. If he is cheating he would surely reveal the cheat on a lower max bet (less than 1 euro) and the website must surely be stopped.
Note that even if he is not cheating (which is what I think) the kelly criterion is known to be quite aggressive (in the world of poker online for example), and again if you run some max betting simulations you may see that some of them are quite scary from the point of view of an investor.
Of course I cannot make other important considerations on lowering the max bet, maybe we are to the point that investors could vote for it, for example.