haha, finally somewhere to use my computer science knowledge...well, not really.
Anyway, the Cobb User Guide clearly states that the max displayed boost pressure for the accessPort(v1) is 18.3psi. It explains this as a limitation of the ECU.
Why would that be? A very educated guess is that the stock ECU simply doesn't use enough bits to represent the boost pressure. Since normal pressures are less than 18.3, this is never an issue. Unfortunately this cannot be changed. Basically what this means is that the people who programmed the ECU decided that it would never need to read boost values above 18.3psi.
Also, I am not sure if this is that same for v2.