Pheace: So, do you think developers are going to keep uniquely selling on the Epic store from now on. Or will they still sell on other stores as well?
Yes I do think that publishers (or self published developers) will continue to sell their products through ALL possible market places including Steam, GOG (after long-long time), Epic and others.
As for the exclusive and costly deals between market and developer they were always here: even we had System Shock 2 and other old goodies as premier digital exclusive on GOG.
Pheace: Given that other stores have a higher cut still, they're not likely to sell for the same price on those stores as the Epic store will they? So do you think it's likely they'll sell their game on several stores, while having it for a lower price on one of them, or more likely they'll simply sell it for the same price on all of them and pocket the extra income from the one that has a lower cut?
A few will definitely lower their prices on EpicStore and proclaim themselves self righteous publishers who think about its customers first and lastly about money gain. I don't believe that Epic will have nothing to do with it but still. And all others will sell their products for the same exact price here and there. I don't see any difference as in console market where AAA-game is sold on different platforms with different fees cut for the same $60 price.
Pheace: For instance, all those developers who were also selling on their own site through the Humble widget which was 5% or something? Did they sell those games for 20%+ cheaper?
Why are you keep calling them developers? Developers rarely publish their own games except for old legacy games and some other random indie game cases, even the latter require a publisher in most cases (e.g. Dennaton Games to Devolver Digital).
And I don't know about Humble price policy sorry. Selling something cheaper for a time being is a norm be it a sale or special deal with a market place.