I find the OP to be general nonsense. The results of adventures in individual groups have pretty much never impacted the overall story. The only time I'm aware was different, was Murder in Baldur's Gate during the Encounters season, where DM's like me were encouraged to send our results to WotC, where the majority outcomes became the eventual result for the official story. Even then, the individual actions (such as my group murdering the commander of the Flaming Fist, and one of the potential villains) had absolutely zero impact... because it would be impossible to incorporate them all and have anything that even vaguely resembled a sensible story.
The long and short of it is, AP are believed to be the most profitable product because that's what the majority of D&D players/dms want. We made it this way, and WotC is only providing us what we want. "We" meaning the D&D community as a whole; there are many (like me) that are in the minority and don't want epic APs. Well too bad for us... WotC is a business, and their job is to make money.