In the USA, car makers have to provide work shop repair manuals - at least they always used to. MB provides that service for a fee, on line. So, they follow the rules but never make it easy to do so.
I expect their EPC is similar. There's one that has everything you need including list prices, dealer prices, changed up numbers, and cross over applications on some parts. While not everyone needs to see dealer prices, they could make it a whole lot easier for the average Joe by providing the exploded parts diagrams. No prices, just item numbers like the old dealer's parts books from years past. I agree though, this is a company that's very anal about almost everything.
MB has a way of looking at anyone who isn't a factory trained tech as being a hack. They won't admit it but it's still there in the background. Hence their resistance to providing anything more than they have to.
Of course, I could be all wrong. ( roll MS tape in 3...2...1 )