I also thought they were useless, that they weren't necessary because we have been playing for years without the need of things as such. However, I just can't get enough of them lately. XD
I have a lot of new games that I still haven't played. I like to buy the games I see I like and have them there for the moment I feel like playing them. With so many games I need something that can tell me that I already did what I needed to do in order to finish a game and pass to play another one. To me, eaning a Platinum is equal to finally nailing a game in this generation. I like to unlock and finish everythin in a game but, with all the games I have and need to play, I feel like I need something to let me know when to stop playing a game and trophies serve this purpose.
I always thought that we needed some way to brag against other people how we defeated a Weapon in a FF, guess Achivements and Trophies can help us out in that. lolz Hope the 13th has at least one.
Nintendo is selling their IPs to Microsoft and this is true because:
http://gamrconnect.vgchartz.com/thread.php?id=221391&page=1