[Anvh]

The results I had with TTL on film were consistently satisfactory, not taking human error into account. Perhaps you are right that it doesn't work right in all circumstances but the method of measuring flash during exposure is theoretically more sound than measuring before the exposure when changes can still occur.
I guess the main reason for abandoning the system is cost. Flashing twice is cheaper than incorporating extra lenses and sensors in the camera.

I meant something different.

They can meter off the film but the surface of a sensor is very different and they couldn't get it to work like it should for digital.

[Twarp]

They can meter off the film but the surface of a sensor is very different and they couldn't get it to work like it should for digital.

I've been pondering a while on this. In a way it doesn't make sense. TTL works rather well and for me great on film which can be found in a lot of different colors and textures, depending on brand and make of the film. Thus differences in reflections measured by the TTL-sensor can be expected but still creating acceptable results.
A sensor however is (a) constant, it is always the same, always behaves the same and therefore should be expected to give very predictable results, i.o.w. theoretically perfectly suitable for TTL. Only reason I can think of is when the sensor behaves as a black hole and simply not enough light is reflected to a TTL-sensor. (Or the sensor itself could be used to measure the light in realtime to shut off the flash but this is a different discussion I guess...)

Meanwhile I've been shooting some slide-film with my Super A and recently acquired Super Program (I like chrome versions and this one is seldomly found in Europe) using the old AF280T and the newer (and only as P-TTL supporting listed) AF-360FGZ and BOTH work fine in TTL-mode! At least the flash unit is 'downward' TTL-compatible which IMHO is a more userfriendly -even foolproof- system than P-TTL. And will boost using the analog stuff a lot

On the other hand I'm getting the hang of the P-TTL mode on the K-x. It just takes some experimenting and deciding on your preffered presets. Perhaps an upgrade to a K-5 to program flash settings in the User modes is an option...