all leased anyway

Why are Mercedes holding back on developing/introducing a potent diesel engine like the 35D Series BMW's and 3.0 Bi-TDi Audi engines? Even VW are getting in on the act now with a 2.0L 4 Cyl 268bhp Engine that will return 60mpg! Yet give a sub 6 second 0-62mph. It's not as if this is new...