Standard bulb is a 12v 10w. Vibration and too much voltage decreases the bulbs life. Make sure you have a 12v bulb in, and check the connections to the tail light. If there is a bad connection, it will be like turning the bulb on and off, decreasing the life.
If the regulator blew, both the head light and the tail light would go together, as soon as the bike revs past idle.
Electrical devices only draw what they require, not what the source can put out. Therefore, the head light will only use 30w +/- 2w for voltage and resistance differences.