They are saving the charging of him for when/if he becomes the GoP candidate in 2016.
Actually, the judge in the case made the determination not to issue an arrest warrant. He will issue a summons instead. This means that Perry still gets his day in court, but doesn't have to be booked and get a mug shot done. Dems all over Texas are in mourning.
The court date will be arranged between the judge and Perry's attorney. I'm sure Perry's attorney will be pushing to get an early date so he can request to have the charges thrown out quickly.