Mark,
Medium format isn't that expensive. Most couples are not discerning enough to go for a format based work - they select a photographer based on his portfolio and recommendations mostly.
Since the digital boom, the market for film based wedding photographers has clawed back: couples can get their spotty nephew to shoot "documentary wedding photos" with his latest digicam. Producing work which can withstand decent enlargement to 20x20" and not get pulled apart by insufficient megapixels helps. Having a touch of originality helps: with the digital hordes, that is becoming harder.
The advantage of digital is that it has brought the costs of wedding photography down for the pro' as well the couple. There will always be couples who want the Walmart approach to their images and the digital capture medium with its erase-re-record facilities is suited for that. It is also faster to get cheap snapshots and jpegs on the web for the couple to view. The spotty teenager can do all of that pretty fine too: so none of this is an argument for quality of the imaging.
The advantage of film based medium format is not just the quality; the tonality of the images overwhelms 35mm and small digicams of 12 megapixels. It also enables specific 'looks with specific film i.e. Astia; Kodak 400VC and Fuji NPS/NPC. There is much less post-imaging manipulation involved.
You might want to look up the Annabel Williams series of books on weddings. That L glass may well be redundant in 5 years; look at how many wedding photographers continue to use their 30 year old 6x6cm formats...
Good luck.