Firstly, this has nothing specifically to do with L:RB (though several of those songs won't play in L:RB anyway because they're not "family friendly")
It should also be noted that the Country and Metal pack exclusives don't seem to have been "officially" rated at this time. Probably because they aren't in the music store for the game to check against.
Tiger Uppercut: Platinum Artist | Expert: G/B | Hard: D/V Song Count: 831 | Newest: "Great Balls of Fire" & "Dog Days Are Over"
Yep, I'm kinda living in England and I've never seen the Metal Pack. I have most of the songs from it anyway, I still want it, even if it is just for Motorhead and Rage Against the Machine.
Sorry, UK don't get a lot of support with these track packs. Hopefully they'll be out as regular DLC soon. Luckily some of the tracks are out already, just a pain not being allowed to support a product you want to!