I suspect that the 1:1 claim of the Canon 60mm lens is based on the 35mm format, even though it mounts only to EF-S camera, thus yielding greater than 1:1. Otherwise the degree of magnification would be less than the 1:1 of the 100 macro (which IS based on 35mm), and offer even further confusion to the lens lineup!
I am not sure if I understood you properly. A lens doing 1:1 is recording the subject 1:1 and has so far nothing to do with relation to certain sensor/film sizes. The only thing which is true: if you shoot a small subject 1:1 which fills the smaller sensor (APS-C) entirely, you would require a 1,5:1 (Nikon) or 1,6:1 (Canon) lens in order to fill the full frame sensor in the same way with the same subject.
Personally for me full frame vs cropped sensor is not really a big issue. More important issue is how well it is executed. Nikon already took care of the wide angle disadvantage with 12-24mm and 10.5mm DX lens.
I still know some film shooters who really like their fast primes (in which they have invested a lot of money) a lot. Some of them consider switching to digital finally, but not all of them would be happy to exchange several f2.8 primes (14mm, 20mm, etc.) for those few and slow APS-C 10/11/12-20/22/24mm zooms. Add the price for a new APS-C fisheye and the 5D is already a quiet good deal. I don't say these zooms aren't good, but some people who would spend the money for cameras like the 5D might love to continue using their fast glass. From one point of view I would even prefer APS-C wideangle zooms because the have a lot more DOF than a full frame lens with the same FOV and therefore perform better behind dome ports in this respect. But I can not confirm that FF wideangles deliver poorer corners in general. I think we have been spoilt by FF lenses on cropped sensors where corners weren't critical because the lenses had been designed to cover a larger image circle. But APS-C lenses have shown the same effect now as they “just” cover the used image circle, like FF lenses with slides or FF sensors. I can not see the Canon EF-S 10-22mm beating all full frame L glass wideangle zooms and fast primes (17-40mm f4, 16-35mm f2.8, 20mm f2.8, 24mm f2.8, and so on) to replace them with just one slow zoom. I am sure Nikon shooters had more wideangle choices when shooting slides than “just” one equivalent 18-36mm f4 (12-24 on APS-C). I am sure Nikon will add more good glass to their DX line but for the time being, it’s not the worst thing if you switch to digital and simply continue to use your existing glass which is not only available now, but already owned.
Don't get me wrong, its looks like a really nice camera with a lot of advances.
But for a camera with that price tag ($3299) It’s looks odd that there are some important features(at list to me) that aren't there but they are in my 'entry level' camera that cost 1/4 of the D5.
With film bodies it was simple, the next more expensive camera was better in most every aspect (frame rate, build quality, etc.). Resolution and sensor size was the same with all cameras: film. With digital we have to face different models being different kinds of compromise between the old days’ criteria and the digital part of the camera (sensor size / resolution). 5D’s priority is nothing but FF and resolution. So I would not say it’s odd that it doesn’t feature certain things just because of the high price. A 5D with Nikon D2X body and features would not be available for 3000 bucks, the 5D sensor is much more expensive than the D2X sensor. On the other hand a studio photographer with no requests to speed but resolution could say the Nikon D2H is so overpriced, just 4 megapixels for the same price like the 5D? Different Cameras for different users with different preferences, hourses for courses. Judging from the very first responses, it seems that the 5D could be a quiet attractive compromise for Canon underwater shooters.