Budget Airline

I am planning to fly to Hong Kong so I survey various way of getting great value air tickets. After much reserch and price comparison, I settle down to Jetstar and book the air ticket through On-line.

The booking system is easy and friendly and is very similar to other online ticketing system for other airline other than the seat selection step that was a surprise to me. It shows me 3 type of seats. S$30 for a great legroom seat, S$18(if I am not wrong) for a upfront seat where the few rows are nearer to the front of the plane and finally S$3 for a standard seat. I am surprise, I need to pay extra S$3 for a seat. Does that mean that I can select without seat and stand throughout the flight? It should be part of the ticket pricing as who will get a air ticket without seat. I understand the extra legroom seat and upfront seat but not the standard seat...

Does anyone know?

One more, to save some more cost, once should do offline payment as I understand it will not charge the S$14 booking and service fee (a friend told me this).