If that was the case, you'd see the 5D Mark II at all a lot of sporting events, and I'd wager that just isn't the case at all. A major sports photographer is not going to se a 5D II when they can use either the 1Ds Mark III, 1D Mark III, D3 or D700.
Sporting events will always be the high FPS, fast AF cameras - namely 1D3 and D3 series. It's a bit of a niche market, and you're right, if you need outright speed, you don't buy a 5DII (or a D300). I'd hesitate to add a D700 to that pile, as although the AF is good, its not at D3/1D level. Colleagues of mine who do shoot sports are all pro-level bodies, although they have the odd 5D/5DII/D700 in the bag for wides.
If all that you said was true, I wouldn't read tale after tale of Canon users dumping their equipment for Nikon, usually a D700 or D3. Obviously, there are some Nikon folks doing the same for a 5D II, but the river is running both ways at a strong clip. A lot of Canon shooters were and are dissatisfied with the autofocus not being significantly improved from the original 5D and with the mediocre build quality. You also can't conjure up a faster framerate, no matter how good a photographer you are. I'd say 3.9 is good enough for most uses, but not for a sports photographer.
Tales are never really accurate - internet postings are full of "I swapped for this that and the other", but you never hear from those who are happy. Once again, using the other photographers I know (FYI they are press photographers shooting for national papers, agencies and so forth) and can hence actually almost do a "poll" of users who don't post their kit preferences on the internet, the 5D Mark II is doing a roaring trade. Yes, there's been instances where they've gotten soaked in the rain and failed (but then the bloke who killed his pair knew it was likely to happen), but then there's cameras that have been around since launch, being treated like every other camera (ie: bashed about) and working fine. As for the FPS, 3.9 is enough for most instances, and when you need more, everybody I know has a 1D on the other shoulder.
The D700 is simply the more versatile, able to shoot well in just about every situation, with resolution as its only weakness (and 12 MPs is plenty for all but the most specialized of shooters; people were doing great things a few years ago with half that). The 5D II has to stick to the sidelines when it comes to sports and fast action.
So does the D700. If you've got a D3 and a D700, you'll pick up the D3. I'm not saying the D700 is a bad camera though - if it was a few hundred cheaper then I think it'd have a very convincing case. As we said earlier, 3.9fps is fast enough for basically everything except sports - my 5D2 is certainly getting a lot of use these days in a varied set of circumstances.
So what do I make of each story that I see of 5D II owners switching to Nikon now, let alone in the future?
Realise that there's loads of people not switching, people buying into the system new, or people going the other way round?
This "dominance" you speak of is imaginary. The three Nikon full frame cameras are every bit the Canon cameras equal, and have been selling just fine. There's no dominance for either brand, unless you want to talk about sports photography. In Athens, it was about an 80-20 split for Canon. In Beijing, it was close to 50-50 just four years later. I saw pictures from both events of the photographers, and there was as much black as there was white. You can thank the D3 for that.
This dominance existed up until the D3 launch, but still sways slightly to Canon. The D3 was great, but lacked resolution to combat the 1DsIII, which the D3x now does. The 5DII then offers that D3x high resolution, but at a third of the price. The D700, being a stripped down D3, sits a the bottom of the range. I personally think Canon are missing a trick by not having a cheaper, lower resolution FF camera (EOS 7D or something, 14-16mp etc) to reduce entry price to FF.
As for the Olympics, you do realise Nikon loaned ********s of kit out to try and convince people to switch? I got sent a pair of D3s, bunch of lenses etc as a month "trial" at that time, despite the fact I wasn't attending. I'm still seeing a majority of white lenses, although the D3 certainly has slowed/stopped the "bleed" to white and given Nikon a damn good platform. I find those who remained with Nikon in the "bad" years are now happier with what they can get (ie: a good professional system) and the rate of switching between either systems has slowed. Most of the turnover seems to be amongst those amateurs who seem to have more money than sense (after all, £10-15k investments in lenses is far too much to just chuck).
