Here's what you're probably referring too:
"
Mercedes-Benz
Mercedes-Benz does not warrant its diesel engines (apart from a very small number of units fitted in German taxis) for biodiesel/RME use."
http://www.channel4.com/4car/buying-guide/faq/biofuels/biofuels-9.html
Problem is..., EU is already at b2 and going towards b5 and better. Germany is trying to out-do France in regards to biodiesel production output. Many stations in France sell B20. I suspect most people regularly use RME fuel at some percent anyway. As stated above, it's just another way to claim warrantee void.
Biodiesel is FAR from Burger King grease BTW, most in EU is from virgin oilseed stock (Rapeseed/Canola, hence the RME - Rapeseed Methyl Esters.)
Meant to add this:
"Country music legend Willie Nelson powers his new 2005 Mercedes-Benz E320 CDI with B100 biodiesel, and his wife Annie has used B100 in her Volkswagen Jetta TDI wagon for over a year. "I am absolutely a fan of biodiesel," Nelson said. "I use it in my car because I'm a firm believer in using renewable fuels that are better for our environment. We should all be doing our part to reduce our reliance on foreign oil and contribute to our own economy. On top of all that, biodiesel use helps our nation's family farmers, while preserving the land for future generations."