I admit that sometimes achievements and trophies can affect my difficulty decision. When I played through Halo: Reach I choose the normal/default difficulty in part because the achievements for completing chapters could not be earned on easiest. I am currently slugging away at Record of Agarest War one more time - having gone through Normal already but on Hard now to see the true ending. Then again, sometimes for games like Madden, I turn up the difficulty most/all of the way just because there is no storyline really, and I need a good challenge.
When talking to my buddy at work, he said he plays most of his games on easy - like Call of Duty. It is not that he is a bad player -in fact, in multiplayer he's about the best I know in Black Ops and Modern Warfare, often finishing tops on the map, but for him he just wants to sample the storyline in single player and then move on.
I also really like difficulty adjusters in general. Would games like Demon Souls be less appealing to people if it had an easier mode? Probably, but does that make it the right choice? I don't know to be honest. I have some friends who proudly puff out their chests at having beaten the game, and I have others who gave up on it or refused to play it due to the difficulty and reputation the game carried. The software developer is obviously fine with this choice as their spiritual follow-up is supposed to be even harder. Will I purchase it? Probably not - the first one frustrated me a LOT at times, and I would rather just play something else despite the fact I did enjoy Demon Souls. If the game had an easier mode where you could still earn trophies and get through the storyline? I'd probably pick it up. It's an interesting dilemma the developer gets to figure out for themselves.
I read a report a few months ago that most players do not finish their games. The vast majority of games have something like a 30-40% completion rate, and many of them in the 20's or lower. If I was a developer, I would be a bit disappointed if I put all of that work into a game knowing that most players never saw the content I made. Personally, I like the idea of multiple difficulties and still offering 'rewards' for people who best the easier ones, though there should be better rewards for the greater levels of difficulty.
What about you? Do you like multiple difficulties? If so, are you someone who always goes for the hardest, sticks to the defaults, prefers less of a challenge or vary it by title and number of playthroughs? Any games out there you wish had variable difficulties but did not?