There are already RPG systems with non-linear probability distributions. GURPS has you throw 3d6, which is a rough approximation of a normal distribution. A +1 in 3d6 gets you to 63 % from 50 % and to 95 % from 91 %. The Fudge RPG system uses nonstandard dice which also have a distribution like this. It's not the decibel system, but it has the behavior you described and is usable without numeric tables or calculators.

Explicitly using probability decibels in game rules might be an interesting way to teach people to work with them though.