2 days of PS3 Trophies and Counting

For the last 2 days I've now been hard at work getting some of the achievements trophies which are now available in some PS3 games since the last firmware update. And since the only game I have that supports trophies, I've been playing tons of Super Stardust HD again After getting the first 2 for finishing the first 2 levels, I noticed that for most of the trophies you have to get the expansion pack which costs 3.99 EUR. Since I wanted to get it anyway, that's not a big deal for me, but I still think its weird and a bad idea, to be honest, to make only about half of the trophies for the core game.