There's two levels of pricing for OEM parts. First, the company makes more, in terms of profit margin, on part than they do on the cars. Second, the dealership's service operation also views parts sales as a profit center, particularly if they're being subsidized by manufacturer's discounted or free maintenance schedules.

I hope the price comparisons in this thread are for the OEM Mercedes parts and not the "OEM-like" or "OEM-quality" parts.