Well, yes… I'd agree that there is definitely a point of diminishing returns – specifically, a point at which the meager profits from a particular sales channel are not equal to the investment of time, money, and energy required to make the ebook available there in the first place.

… but on the other hand, the "investment model" of digital publishing changes the landscape somewhat from a traditional marketplace. As you've pointed out before, once you put an ebook up on an online bookstore, it can generate steady (if small) sales for *years* without any additional effort on your part.

Is the tipping point of diminishing returns higher for the digital publishing marketplace than in others? If so, then where (thinking long term here) might that tipping point of unprofitability lie?

Is putting an eBook on Kobo unprofitable in the long term? I doubt it.

Is putting it on Smashwords unprofitable? Maybe.

Is translating it into German and putting it on Amazon.de a waste of time? Yeah, probably.