I have been shooting commercially nonstop for the last 4 years, and have had this same debate numerous times. The main things I have always taken away from MF cameras outside of the high mp is the tremendous depth, sharpness, and dynamic range that cannot be matched by and DSLR in the market now. Sure the D800e may have closed the margin a bit, but one still can't come close to comparing. I have gotten a chance to play with a Hasselblad, Phase One, and Leica, and have been even more tempted to make the leap after hands on time.
What I have learned though is that clients could care less what camera you use as long as your are delivering on your final product. Most of my work is print related, and some prints exceed the size of 4'x8', and I have yet to have a client tell me they believe the image may be a little soft. Sure in a perfect world where money really wasn't an option I would love to buy into the MF world, but to be honest my clients aren't asking for it...and the print quality doesn't seem to be demanding it. With the likes of the D800e and whatever Canon is planning on unveiling at the end of this month I don't see myself moving towards the MF market for quite some time.
What kind of work do you find yourself shooting on a regular basis for your commercial clients?