GTA does not need to be an "annual franchise"
Grand Theft Auto titles do not need to be annualized said Take-Two during its Q4 fiscal call to investors.
According to Take-Two, GTA is a strong enough franchise that it does not need a new release annually, especially with the completion of the GTA IV story through DLC proving to remain profitable.
Guess GTA V will be landing sometime in 2011, then.
The call is ongoing, we're listening, and will update you if anything interesting happens.