What wikipedia had to say about tuk tuk- "Auto rickshaws are a common public transportation in many countries in the world. Also known as a three-wheeler, tempo, tuk-tuk, trishaw, auto rickshaw, autorick, bajaj, rick, tricycle, mototaxi, baby taxi or lapa in popular parlance, an auto rickshaw is a usually three-wheeled cabin cycle for private use and as a vehicle for hire. It is a motorized version of the traditional pulled rickshaw or cycle rickshaw."
The tuk -tuk also varies from a mini lorry to just a horse carriage drawn by a motorcycle..
When I was in Siem Reap.. That was what I encountered. The tuk-tuk there was in reality a horse carriage drawn by a motorcycle. I got on almost similar type of horse carriage back here in Malaysia at the Titiwangsa park drawn by horses or was that at a zoo somewhere...
Then in Bangkok, the tuk tuk is different. It is like a mini capsule or truck with openings on the left and right.
And then I was forced to take a tuk tuk in Surat Thani to my hotel and again to the airport. This one was actually a mini lorry. And the entrance was from the back.
It shows that there are different types of tuk tuk all over the world. Forgive me if I may seem a little dense here to some of my other more better traveled friends but it is just what I discovered. And it also proves I should travel around Asia more... Hehehe