I think there is a thin line as to how many people can sit in a car and how many people can travel comfortably in a car.
Four of us, (A friend, his wife and my wife and me) went to Ooty on a 3 day trip in my Zen. I had to pull my seat a little to the front for the back seat drivers. We made it. I drove all the way. Could I drive in that position - Yes. Was I comfortable driving in that position - NO.
Five of us went to Chennai in my Manza. The two girls and a guy at the back were very slim. When I asked the girl sitting in the middle if she was comfortable she said yes.
While coming back there were only 4 of us. Two girls in the back. And the girl who was sitting in the middle on our onward journey commented "Wow, this is great, what comfort" with the rear armrest in position. Both the girls enjoyed the drive back.
Though the car can hold 3 people easily in the rear seat, the comfort level is meant only for 2.
I hope I have made my point clear.
Even in Punto and Swift, with the front seat pushed back I find it difficult to even get in, leave alone traveling. Even my old zen had a lapbelt for the middle seat. In some cars there are also 3 headrests.
Even in a bus which has a flat 3 seater, you will be comfortable if only 2 people are sitting. Of course 3 people can sit. But will all the 3 be comfortable? OT
Back in 95 there was a competition by Maruti as to how many people can get into a Maruti 800. If I remember correct, it was more than 40