Originally posted by Macario I do not think so, so let's see if I get what you are writing
Do DSLR manufacturors have to produce big fast zooms? Yes, because they will generate money for them.
Does a consumer have to buy one? No, if he doesn't need it.
Do DSLR manufacturors say that you need big fast zooms otherwise your FF will not deliver. Yes, as it makes money for them.
Does a consumer have to buy one? No, as slower smaller zooms, or even primes might fit their budget and/or requirements better. And they will get results which will be more than good enough anyway.
I think the question is who buys a *large* full frame camera, that also happens to cost 3500 dollars? It may be a budget conscious individual who buys it to mount his budget prime collection on. I doubt this is the case generally. More often, it will be someone who wants "the best" and doesn't care about size. In fact, they see their big lenses as signs of their virility and show them to be above the common APS-C SLR user.
To me, the question really comes down to whether or not you need the narrow depth of field full frame offers. I venture to say that after cropping, post processing and other standard manipulations it would be hard for most people to pick out the difference between these two formats.
To me, narrow depth of field is a side effect of opening up wide aperture lenses in order to get decent shutter speeds. It is not its goal. I have already had the experience shooting a couple at f2-ish in lower light and had the guy in good focus and the girl really soft.
It is clear to me that APS-C gives me one stop more depth of field for the same shutter speeds and that, in general is a good thing. I can understand wanting something different, but I don't really understand where the goal of "as narrow depth of field as possible" started.