Originally posted by Serkevan Technically the 20-30fps are clearly advertised as working *only* on a specific set of lenses (not even on all Sony lenses). Any other lens is explicitly not covered by the spec and works at the lower frame rate.
I agree that it is somewhere between disappointing and scummy (depending on how much one believes the official reason of the excluded lenses having aperture mechanisms that don't manage 20+ fps), but I would say it isn't misleading. And besides, if one pays 4000€+ on a camera body because 20 fps is a core competency... Why are you cheaping out on the lens? It's a bit like complaining that the Eye-AF of the K-3iii doesn't work with A-series lenses, or (less tongue-in-cheekly) that it works pretty badly with the old F-series macros.
EDIT: I just remembered that Nikon was doing this a while ago with their own lenses as well - the D6 (and D5 IIRC) is capped at 10ish fps for lenses without electromagnetic diaphragm, they only let you shoot at 14 fps with electromagnetic apertures. This also applied to older models from Canikon, where the High burst rate was locked behind having the battery grip installed.
Obviously all of the brands will try to push their users towards new, more expensive lenses. Third party lenses, while often cheaper and beneficial to the end photographer, are not appreciated by the brands.
I guess I would prefer that the encouragement would be more positive, in that the newer lenses are sharper, have better image stabilization or some such feature, rather than simply that the brands artificially slow body performance with them. I think Canon and Nikon are pretty happy when a firmware update makes it so third party lenses don't work as well.
Pentax hasn't really done this to this point. They release lenses that are no longer compatible with old film cameras, but they haven't taken screw drive motor out of any of their cameras, even the cheapest, entry-level ones.