Difficulty and Length of Games..

Why does it seem like these day games just get harder and harder, is it because we are getting better and better and we need to stay entertained?  Games like Star Wars: The Force Unleashed when on their hardest difficulty I can barely take 6 steps before being shot into oblivion, yet they base so many of their achievements and unlockables on this difficulty.
Doesn't it also seem like games are getting longer but also shorter? That might not make sense to some but it means "They are getting longer but are keeping the player entertained for a much shorter time period. It might sound a little wierd for me to say this but I never finished Halo 3's campaign mode because I saw how much fun people were having in the Multiplayer, same goes for Gears 1 & 2, and Call of Duty 4 ( I tried to finish it but my friend wanted it back). 
So maybe it is better for games to be filled with content that only lasts 8-13 hours instead of 15-19. This may just be me talking randomly but this is what i feel its gonna come down to.