You really can't prevent "when does the new mIRC comes" questions.
You can inform users in multiple ways.
With a release date or without.
When you choose to give a release date, you are creating expecations. However, when you don't release it on the release date, hell breaks loose in the form of whining.
When you don't give a release date, people still will wonder when it comes out, or say stuff like hurry up.
So IMHO I think the current "release policy" is the most efficient.