Historically, yes, the types of buyers looking at the C-Class and the 3 were very different. MB have tried hard to make their cars better to drive and more attractive to the sort of people that would normally buy BMWs, and there are a number of people on here looking at both. Plus with some of the ridiculously low leasing rates MB are offering at the moment getting into a C-Class can be cheaper than the equivalent BMW.
Current: F30 318d Sport manual, AW, 18" alloys
Sold: R56 MINI Dooper 2010, Chilli, Bluetooth
Sold: E93 325i M-Sport auto 2007
Sold: E91 320d SE 2005
Sold: E46 318Ci Coupe 2002