whatsnottaken: But it was never a Steam vs. GOG issue if it was available on both (also in the humble store) it was Steam AND GOG. Even with little to no sales what would be the point in removing it unless he was simply not seeing revenue come in from those sales.
You're essentially reiterating the point I was making (and to my own failing, I don't know how to make any point well) - the general idea was that to him (and a lot of other developers) the exposure their game(s) see through Steam tends to be higher than that of GOG and in turn warrants a substantially bigger amount of copies sold over time (which is not to disparage the way GOG handles anything - this year alone, with the bump in sale frequency, it's clear that they're attempting to bring exposure to the titles in their library which hopefully helps change the minds of some devs about the general climate here).
When indie developers do their post-launch/etc. write-ups, often with accompanying sales data, it's often the case that if they've sold their game through Steam, it accounts for a huge chunk of their sales while the "smaller" (for lack of a better descriptor) outlets bring up the remainder (and often in the single digit percentages). With Pony Island, the unfortunate business of the original distributor going bankrupt a time after the game had launched no doubt just compacted the notion for Mullins that selling the game through GOG wasn't going to yield any amount of return that he was comfortable with.
Maybe I've just read too far into what Mullins' response as relayed through Darvond's post to this thread was. Maybe when he cites "lack of interest" he just means exactly that and not "sales weren't where I would like them to be through GOG".
Personally, I hope he eventually reconsiders and works out a new deal with GOG when he has the spare moments to do so.