most hobbyists I know - including many with a 5D 2 - own not more than 2, max. 3 lenses (kit + telezoom and/or portrait fixed focal) and possibly (!) one Speedlite. For many of them switching to another camera supplier is not really a hard decision. Pro's typically do own much more and more expensive gear plus are quite dependent on their in-depth experience using it plus their established workflows as well as factors like good contacts with CPS (or NPS on the Nikon side) ... for many of them a whole lot tougher to change horses mid-race.
It's tough to generalize like that. I know lots of pros whose gear is limited to a primary body, a backup body, and 3-4 zooms. Some might only have 2-3 zooms along with a couple of fast primes. It's true that they make their money with their gear, but I don't know a lot of rich, full-time photographers. I depends what type of pro you're talking about, too. Sports photogs might have a ton of gear, as you suggest, but a photojournalist or wedding photog might be limited to a small handful of zooms and primes. Hobbyists, on the other hand, cover the gamut from a soccer mom with a kit lens to people with loads of disposable income with several Pelican cases full of gear.
You do make some good points about pros being less likely to switch. For one, a lot of pros are out of touch in terms of the latest and greatest gear on the market. A lot of pros look at me like I'm crazy when I mention the strides Nikon has made in the last 4-5 years, and how they're putting out an outstanding product line now. Plus, as you suggest, familiarity with a system is very important as well.