Fun with math

[Eve]

That the curve is not symmetrical is not an effect of wrapping. In fact, you only get a symmetrical curve when the chance of succes equals the chance of  failure (eg n d10@5). This is binomially distributed though. A normal distribution is never possible with dice, for the very reason you already mentioned: there is always a minimum of 0 succes (as well as a maximum number of successes).