EMT is used because while the technicalities regarding the term are not always understood by the customer, people are generallya ware of the term and it is regarded as 'a higher level course' and then easy to search for. The US EMT-Basic course requires 180 hours of learning ( IIRC) plus work placements.
It actually depends in the US as well. Some states have slightly different set ups. Also they tend to have a better course set up, it is easier to build up to the 180 hours. For example, a fireman would have some of those hours by default.
It is almost impossible for a civilian in this country to become an Ambulance Tech, let alone a Paramedic. The only way to get the training is to do the job full time. Depending were you are in the US anyone could be a EMT, a lot of professionals will have a minor skill.
I surpose the big difference is that in a lot of places, you are not keeping someone alive for 8 minutes, but doing everything possible to make the golden hour longer. That would be the difference for me, if you can call an Ambulance and expect it arrive on target, that is normal first aid. Any time you are thinking I am not even going to see someone else for an hour, it would be wilderness first aid. While that would take work to do in the UK, in the states driving down the road could put you in that position.
I would really like to see someone on that website mentioning some of the you cannot use this in the UK etc. It seems very sell the course, and keep the facts out of it.