I believe it defines 'normality' by how many of your interests are shared by how much of the LiveJournal community as a whole. As most of your list comprises bands that, chances are, most of the other users worldwide haven't heard of (not being British and all), so we're made to look less 'normal'.
If we all put down stuff like 'reading', 'writing', 'films', 'music', etc - really generic stuff - we'd look a lot more normal.

Alun