Nota bene: there is a meaning difference between "more than any X" v. "more than any other X." For example:
1. Alaska is bigger than any US state.
v.
2. Alaska is bigger than any other US state.
The 2nd sentence is the correct one. "Any" implies that Alaska is outside of the group "US states," and is bigger than any member in that group. "Any other" implies that Alaska is in the group "US states." Since we know that Alaska is a US state, the meaning of the 2nd sentence is the correct one.
HOWEVER - this is something that the GMAT is very unlikely to test you on! In the Kroetz sentence,
his works are produced more often than those of any contemporary German dramatist. => Kroetz is NOT a German dramatist.
his works are produced more often than those of any other contemporary German dramatist. => Kroetz IS a German dramatist.
The GMAT could hardly expect a test taker to know whether this guy is German. (His name sounds German, but he could be Austrian, Swiss, etc). Since the meaning difference relies on outside knowledge that you couldn't be expected to have, this was just a red herring.
Ceilidh Erickson
EdM in Mind, Brain, and Education
Harvard Graduate School of Education