I guess the 48k mile service in the UK is the same as the 45k US service. My car has got the ASSYST feature; however in the service manual it says that after 48k miles you have to have certain additional work done at the next service. This includes a coolant change, tighten some steering components, fuel filter changer, air filter change, and some other stuff. Yet more cash...(!)
BTW, what colour and trim level is your C280? As I've said before, I wish I'd spent an extra 50 quid a month to get a six cylinder. Duh. Maybe next year, when I'm a bit more insurable, I'll get a C43, prices are falling fast here.
Also, since you compared UK/US services, I think it's interesting to compare the UK/US Mercedes attitude and also the attitude to cars in general. Your US techs and dealers seem much, much better informed about very technical aspects of these cars. The range of products and services available is also impressively more extensive: the fact that you can show up at a car outfit (Circuit City) and they'll know how to fit your illuminated door sills and moreover will do so for just $60 is amazing: this just does not exist in the UK!
I'm a bit jealous about the Californian weather as well!! I spent a fortnight there two years back: what a place... you've got civilisation cracked there.
On a side note, I ran at speeds up to 130 in tow behind a Boxter at the weekend--he had the roof down. Car was rock solid on the twisting but smooth A1 in Yorkshire. Blew me away after 20 mins, my car was flat out (that little 2 litre just not up to it).
1999 SL 500
1993 320 TE
1986 500 SEC