The drive train has a lot to do with the classification. VWs were rear wheel drive, same as many of the cab over vans. Most minivans are front wheel or all wheel drive.
I mean, what are the counterexamples?
-the body-on-frame/rwd/solid axle Aerostar/Safari/Expo were...slightly smaller than the domestic quarter ton vans. not really mini, plus all the drawbacks of high floor height, bad fuel economy, truck handling etc. of the full size vans.
...which is why they aren't sold anymore.
-the VW Type 2/Vanagon:
Customers didn't like rear-engine handling. Or two-digit hp in a 5000lb gvw vehicle. Plus it's hard to make forward control layouts pass front-impact tests. So, a design dead-end.
-Mid-engined Japan-vans
High floor height, weird service position, once again, crash safety became an issue.
Of course, I'm happy that all these vehicles existed, and surely many customers felt their advantages outweighed their deficiencies...but on the whole, the Chrysler model ended up defining the market as it exists today, in the same way the Mercedes W124 defined "luxury car".
(Edit: missed gvw when I wrote this, but it's unusual to typify a vehicles P/W ratio by GVWR. That's more a comment on its structure and suspension.)
Had there been the Oettinger flat-six available in US-market transporters from the beginning, perhaps the minivan market would've turned out a little different....
Wanna know why inline fours bolt up so nicely in Vanagons? Because VW originally intended to put an inline in them. I mean, do you really think VW wanted a an air-cooled engine with friggin' ignition points in a 1980 model? And an anemic, decades-old engine design in a 4000lb. (in the case of our Westfalia) vehicle?
Had VW not done their usual (IMO) half-assed planning and design, it might have been different. But then they wouldn't be VW, would they? :-)
It doesn't mention Westfalia models directly, though, unless they're one of the model numbers in the breakdown.