Sorry, but it is not actually a fact. A larger format simply has larger pixels spread over a greater area, that's all. Assuming you frame the same subject the same way, with the same physical aperture, the 35mm sensor would perform the same as the MFD sensor. It's called etendue. The MFD sensor might have a potentially higher maximum saturation point (FWC), however what actually matters is how much light actually reaches the sensor. With the same physical aperture, both the 35mm and MFD sensors would gather the same amount of light...since it is the lens that captures light, it's front element doing the gathering and the aperture controls how much of what was gathered actually reaches the sensor.
Put the same number of pixels on subject (i.e. fill the frame and compose the same), and for the same aperture and exposure time, S/N of the resulting image will be identical. The only difference would be ISO, which doesn't do anything other than change what number of electrons constitute "maximum saturation". You would need to use a higher ISO in the MFD than with the 35mm sensor, but both would produce identical pictures with the same noise characteristics. The MFD lens would have to bend light more, so you'll have a greater problem with optical aberrations, which ironically would actually give the 35mm setup the advantage.
Please, read this article before you continue insisting that MFD is just plain and simply better without question: http://www.clarkvision.com/articles/telephoto.system.performance/index.html
Roger Clark argues that the 7D is actually better from a "gathering detail at the same S/N" standpoint than a 35mm FF camera, but the same argument holds true regarding FF and MFD, as the two have about the same difference in terms of ratio of area as an APS-C and FF do.
Thats all fine an dandy but your excluding what make's Medium format what it is.
Its much larger than 35mm, thus has more area to stuff more pixels than 35mm!
That fact alone means that any thing 35mm can resolve can be done better on MF. This fact hasn't changed and will never change from film to digital.
RLPoto you are mixing up things, if the sensor from a MF where equal to 24x36 in design, QE, DR etc then you are right. Bigger is better, but todays MF ccd sensors from Dalsa is years behind, not regarding resolution but efficiency, noise, etc.
Those factors only really affect the lower (darker) fraction of the signal, and only matter if you actually need to lift highlights. In my experience, people who use medium format are far more interested in their larger pixels, which allow a larger FWC than comparable 35mm FF or APS-C sensors (although these days pixel sizes are down as low as 6 microns in MFD...so maybe the pixel size lead is diminishing), along with 16-bit ADC, and thus allow very rich, smooth, and down right legendary highlight preservation and fidelity. I've never heard anyone who uses an MF digital camera complain about shadow fidelity, but I've heard them complain about poor highlight retention in smaller formats.
There is no denying that medium format cameras have a lot of advantages, stricter quality control mechanisms, higher precision and higher quality counterparts (such as image processing chips), and a lot of other features that simply don't exist in the DSLR field (such as interchangeable backs.) But that does not mean that medium format cameras are unbeatable in every respect, or even that they resolve more detail (which is simply false).
There are pros and cons to every option these days, but there is no question that 35mm FF DSLR's are beginning to encroach upon MFD territory. In the case of the D800, and assuming the rumors are true, even more so with Canon's 46.1mp prototypes, are and will pose a serious thread to MFD in terms of IQ. Canon is known for favoring the highlights with their default tone curves, and if they release a 46.1mp sensor with 16-bit ADC and low electronic noise floor, they could definitely give the H4D-50 a run for the money. Especially when paired with Canon's new Mark II series of lenses, which use nano-tech anti-reflection coating, some of the most advanced optical designs and materials in the world, and some of the largest physical apertures in the world.
De-facto statements like "MFD is just plain and simply superior, its' fact, don't argue with me, I am an anecdotal freak but I don't need to use facts" are just plain naive. The real question is...will the advancements being made in the DSLR sector spur a new round of innovation and advancement in sensor technology for medium format digital? Will we see reductions in read noise, further increases into the 100mp and greater territory, higher bit depths, etc? Or will MFD finally lose it's footing, and lose out to the new wave of 30, 40, and 50 megapixel 35mm FF sensors that outperform in every respect?