Cebu-Pacific Air - Wtf?

I am arriving March 10 and after spending a night with a hot new find in Manila who is seriously bi- and into three-sums (if she ever show's up), I am planning to leave for Davao to spend time with one of my existing gf's. While looking for tickets, I found a round-trip ticket via Cebu-Pacific Air for PHP1812, which is around $42.50. 

Since that is not going to cover the cost of fuel of the A330-436 that flies that route for 1 hour 45 minutes each way, I figure there is a catch somewhere. I will be flying with one 21" carry-on suitcase and one briefcase - they charge an arm and a leg for carry on luggage?

So... where's the catch?