hmm, many questions, i'll try to remember them:
We do have lots of low geared high revving 4 cylinder vans because the weight is a big issue: For anything heavier than 3,5 ton you need a truck license. With all the other paperwork and licenses for truck, you pay about 8000 euro and need to know a lot of technical details about trucks. you allmost need to be a truck mechanic to get your truck drivers license.
A van with a plywood box and a hydraulic load platform will hardly have 500 kg of load capacity left, if its a 3.5 ton vehicle. that's why most of them are 5 ton vehicles (dual rear wheeled Sprinters) which are approved for 5 ton technical, 3,5 ton legal weight.
Many if not all sprinters on the road, are overweight. You can get a fine for it.
What we do at the company i work, is converting these 5 ton Sprinters to 3,5 ton (small drivers license) 5th wheel tractors with air brakes.
suddenly the max. CGVW of the, still small drivers license truck, is 7.5 ton
If the driver has a professional drivers diploma (just theory exam, cost about 1000 Euro) the weight of the 3.5 ton tractor is only limited to the max gvw permitted by the vehicle manufacturer. For a Sprinter this is 8750 kg.
funny thing eh ?

Well this is European law.
It's a big thing in Holland, also because there are more jobs than actual truckers.
Many self employed people drive their lawn mowers and mini excavators around with a Sprinter 5th wheel tractor trailer combination on small drivers license. also rental companies have them because anyone can drive them.
I guess the 3,5 ton limit for the small drivers license, plus the huge cost for getting the commercial drivers license, is the major factor for high revving 4 cylinder vans in Europe.
A 440 kg cummins takes just too much off of the 3,5 ton GVW.....

Also, our lightweight vans consume less fuel than your heavy pickup trucks...
Maybe the lifespan of a Euro Van is limited to 300.000 km, but what professional company would want to keep their vans that long ?
How much are you guys allowed to tow on your passenger car license ?
And is getting your commercial truck license, still as easy as "drive around the corner and back, and if you dont hit something you're passed" as it was when my brother got his license when he was with family in Canada for holiday ?
....Oh ja i remember what i was going to say:
Pipe diameters: Wheel rims, and pipes inner diameter are also measured in inches.