-the mobile carriers cut - up to 70 percent
-the publishers cut (depending on whether you used them). up to 70 percent (carrier fees included).
-some publishers requiring apps to be code signed like Java Verified (a cost that could go up to 50 thousand dollars PER J2ME/JAVA ME app) or Symbian Signed or BREW.
It was a horrific time to build mobile apps.
I am still not defending the 30 percent cut. Just that the cost was seen as trivial then (also the miniscule 99 yearly membership fee that included code signing - Blackberry started at 2500 USD a year).
A simple solution to all this mess is to have rules allowing us to download apps (at our own risk) from outside the app store like you can on Android.