dave,
RVIA is the organization that sets the definitions. They regulate/govern the industry, are their trade group and lobbying arm. They certify that RV's meet the guidelines. Not wikipedia, or any individual builder.
In their definition, it's either a B or a C. There is no B+ regardless of what individual manufacturers claim. A B is a van, a C is on a cut-away. A bed over cab is NOT part of the definition. They just say it's an indicator of some.
The forum is structured the same way. If someone in here starts talking about a B, then the assumption is it's a van conversion. Currently you can get vans in gas or diesel. Not Sprinters, but Fords, Chevy (in years past) and soon Promaster (gas only right now).
A diesel generator is not available from 99% of the builders. Roadtrek, Advanced and the rest are now going with the extra alternator setup. That is because the size requirements of the diesel genset mean that you have to give up tankage size or battery bank - there just isn't room for everything in a B.
The links you provided are old. I looked at the Advanced RV one - a blog post does NOT mean they are offering it. How you get that idea from that text? All it says is they were looking at it - 2 years ago. It is surprising, considering their price point, that cost of the generator was an issue. I'd think it would be the dimensions and the noise factors. Since then, they've been going with the extra alternator. There is a bit of controversy around this choice, which you can read about on a few forums. Roadtrek is doing the same thing on the E-Trek, but you can order it on their other models, including the Chevy.
If sportsmobile is still offering the diesel generator in new builds (which we haven't confirmed they are)that means they are giving something else up. But they are a totally build to order outfit - they'll make whatever you want, generally, if it's a good idea or not. So finding one in a 2010 model is not all that surprising, I suppose anything is possible if someone had the budget.
All your mainstream builders have a narrow set of offerings. Please name one - winnebago, pleasureway, great west, roadtrek, etc, that is offering a diesel generator on new builds. I bet you can't. If you find any links, go ahead and post them.