It's complete bullshit. Just an artificial way for developers to make their game longer. I've been playing games for a long time and I'm good at them. I like a freaking challenge when I play. If I'm stuck on the normal setting I'll blow through a game in no time. I like to crank it to the hardest setting and blow balls all over it. Sure as shit after I finish on normal I'm going to want to try my hand at the harder mode so I go through the game again. When I could be playing something new.
I give credit to the Call of Duty series, Veteran mode is available right from the get go. Same thing with the Halo games, even fucking Halo Wars has Legendary opened at the start. I know more games let you choose the hardest setting right from the start but those are just two examples.
Now two big triple A titles that make you unlock their last difficulty. I'm looking right at Gears of War 1 and 2. What the hell! Another series, Resistance 1 and 2. Just give me what I fucking want from the start. Then on top of the unlocking Resistance 2 was a fucking cake walk on Super Human.
They let you pick easy from the outset so players that may not be good enough or just want a casual play through can get their kicks. Game developers need to understand that a game being to easy can bore someone good, just as a game being to hard to frustrate someone without top notch skills.
I'm not bashing people that play on easy or whatever. I'm just saying it's a dumb thing to have as an unlockable.