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: Skoda Octavia Scout 4x4 DSG
Previous: F30 318d Sport, R56 MINI Dooper 2010, E93 325i M-Sport auto 2007, E91 320d SE 2005, E46 318Ci Coupe 2002