Depends on what you mean by completion.
If it's a narrative-driven game and seeing credits means completion then those developers should care. I've dropped a bunch of games like that where the gameplay was just a repetitive slog required to move the story forward. And if the gameplay is great but they keep interrupting it with a mundane story that's just as frustrating. In either case I'm less likely to buy their next game.
If it means doing all of the side quests and collecting all of the trophie/achievements then who cares? Developers bloat their games with stuff like that because people moan about their games being too short. That's an attempt to placate people who need to play a game for 80 hours to feel like they got their money's worth.
For pick up and play games I don't think it matters.
I always just look at whatever the achievement is for the last level as the indicator. Very true that only a select few are going to complete all the collectable hunting that gets thrown in around the main story.