They did that in Dragon Age too. :p
It takes at least three play throughs.
I have six platinums, and a 100 percent on a game that doesn't have a platinum trophy (I AM ALIVE). Soon to be seven plats, once I finish with the original Mass Effect.
I have eight platinum's and four 100%.
I think the easiest was The Walking Dead. You get one for completing each chapter, so by the time you beat the game, you get your plat.
The six I have currently are
Assassin's Creed II
Assassin's Creed Revelations (Brotherhood has a stupidly difficult multiplayer trophy...it's the only one I'm missing)
Mass Effect 2
Mass Effect 3
My 100% Gamerscore games are:
Guitar Hero Aerosmith
Rock Band Blitz
Guitar Hero Warriors of Rock
Modern Warfare 3
Rock Band 2
Modern Warfare 2
Sonic & Sega All Stars Racing
Call of Duty 4
Halo 3 (Have all achievements except 1 in Halo Wars, "Get General Rank on Xbox Live")
Halo 3 ODST
1 vs 100
So mostly music games and shooters. A note for people wanting to get the DLC achievement/trophy on Guitar Hero Warriors of Rock, buy all the free DLC and you can get it (you don't have to spend MSP/PSN money to get it).
Dragon Age: Origins
Fallout: New Vegas
Ratchet and Clank: All 4 One
The Walking Dead
I almost had Red Dead Redemption but it also had stupid online trophies. And one night when I almost got one, it didn't register for some reason and I gave up. :p
Oh, LA Noire. I have that one, too. So I guess I have seven.
I just got the two Fallout games. And Skyrim. Are they relatively easy to plat?
I would say Guitar Hero Warriors of Rock would be relatively easy to platinum as long as you have all instruments.