why, do certain clients require that images be 50mpx? If so how were they getting satisfying results 5 years ago when highest resolution was 20mpx?
I think it is fair to say that the quality was redefined by photographer's control in producing work, development from the camera/lens maker, sensor developer, software developer, what was accepted yesterday does not mean it will be accepted tomorrow, of course, certain aspect of the quality such as artist approach, character in picture and style, its mood and tone hardly change, and are very subjective. The point is, at least the way I see it, if the client has the choice and option of getting a different quality camera, he may go for it, and such option - for example - a H3D50 vs. H3D39, might be the smallest cost factor in one production - speaking of rental cost. In practical, if a 3 days production cost around 50-100K, including to hire models, production studio, photographer, camera/lens, lighting, the art directors and so on, they might just want to work on what's best or what's highest out there. Quality is not a constant factor, in many ways, it is always a comparison. Sometimes, it is not because what is available is not good enough, it is because there is or there are something better out there.
In my experience, almost all my client never ask which camera we are going to use, but sometimes, as photographer in business, we have in general all the tools necessary to do all the production on hand today, but it is always a wonder that what a higher end camera or digital back can do and would I be able to make use such quality advantage as my advantage. May be it is a challenge of being staying current. And these days, some clients know the latest camera news as the photographer.