I highly doubt Canikon would spend any significant amount of money on astroturfing and risking negative brand impact when it leaks out, when the potential MFDB market is a few thousand units worldwide, while there are millions of dSLRs to be sold...
That's pretty funny.
If your a working photographer, the only "lobbyism" you see on these forums, past some of the obvious brand or format loyalty, is just a single photographer positing what he or she uses to make art and make a living.
As Michael has mentioned this "medium" format section is the closest thing the forum has to a professional section, (same as during the RG days) and what you see isn't a concerted effort to lobby against medium format on behest of Canon, Nikon or Sony.
Camera companies don't pay that much money to photographers that they promote in the first place and no reputable company would put a shill on a forum giving out disinformation. In the world of the 7 year google internet no company would take that chance.
I have multiple cameras, multiple formats and some are good in studio, some aren't, some are great if your shooting slow, some are fast and some are just making less and less economic sense as the business of "commercial" photography changes, mainly because we're not shooting slow anymore and we're not getting any more money whether we have 22, 30, 39 or 60 mpx.
GW is right a lot of the medium format business model is outdated.
To me medium format is a self fulfilling prophecy of difficulty. No buyer asked for a complex buying system, no buyer asked for cameras that are slower, more difficult to learn and that take a flow chart to know what camera back is "allowed" to work on what camera body. No camera buyer wanted to see their Rollei only work with a handful of backs, their Hasselblad limited by back, lens body combinations, or their new Phase with sensor plus, require a return to the maker to add the sensor plus feature.
In fact the few remaining medium format brands, since all are aligned or owned by the digital back makers, have done more to limit medium format use than all the marketing brains at Canon and Nikon combined.
Actually, there are more medium format dealers, reps, and makers on this forum than anyone I see associated with Canon and Nikon.