I don't understand AC/DC and why people like it.
Death metal, like many genres of music, is an aquired taste. When you're used to it, it really doesn't sound all the same. Much like it's possible to dislike some rock bands, and love others.
People say "it all sounds the same" about classical and jazz music too. Why? Becuase they aren't used to it. I'm not saying you should force anyone to listen death metal (or jazz or classical) untill they can tell the differences between the bands/songs, but a lot of the times you'll find that they really don't sound the same. If I said every AC/DC song sounds the same, every Slayer song sounds the same, every Pantera song sounds the same, someone will disagree with me and likely because they are more "used to" said bands than I am. To me, all the songs I've heard from these bands sound the same, but I realize that isn't so for all people. I just don't care enough about these bands to prove me right or wrong.