Well for film and TV thery use focus groups. The focus groups give feedback on what they liked and didn't like and the studio makes changes. No doubt they even make changes to the ending in some cases. Sure it's not possible to change the ending of a movie after it's been released, but that's what remakes are for.
I liked the ending of the original 'Girl with a Dragon Tattoo', I didn't like the ending of the Hollywood re-make, though over all I liked it. See remakes, which I have to pay to see just like the original, can be equated to alternate ending DLC for a game.
Things are no where near as black and white in other entertainment mediums as people like to make out. Bioware wouldn't be setting a ruinous new precedent, they would be evolving an existing practice from pre-release focus group modification of a product to post-release public feedback modification.
I also think authors may possibly make changes to upcoming volumes in multi-book series based on fan responses to plot developments in the published volumes. Perhaps they don;t change the fundamentals of the ending of their story, but they might make non-trivial changes to various plot elements.
“The fundamental cause of the trouble is that in the modern world the stupid are cocksure while the intelligent are full of doubt.” - Bertrand Russell
"When the power of love overcomes the love of power, the world will know peace."
Jimi Hendrix
