oh sorry i meant storing topic info in zookeper that limits kafka to a certain number of topics.

Nope, it also stores topic metadata in ZK - it's not exactly going to store that in the (near) stateless brokers, or in Bookkeeper - and BK also relies on ZK, but it's common to reuse the ZK quorum between the brokers and the bookies.

It also needs an additional ZK for cluster replication.