They did, and it is the only real contender.
Audi have their A6 hybrid and BMW have a 5 Series, but the trouble is they are only better emissions than a high end petrol engine. If you already have a 2.0TDI, then you're getting better CO2/M than the new hybrid.
They make sense if you're swapping from a 3ltr Petrol engine, but if you already drive diesels (as my father does) then they are no better, but with an extra £10,000 price tag.
The Merc actually gets figures that...