The actual tune has been kept the same from BB1 right through to BB4 adverts.
There are no vocals as in verse, verse, chorus, verse, but there is a woman wailing in there - couldnt tell ya quite what she wails though.....
Whenever I hear it, I think immediatly of Big Brother. If they started to change the theme, it would take a while to make the association. I suppose they will have to make the change sooner or later else the tune will sound dated, but for now I think it still sounds relevant even today (well, it has got Oakenfolds name to it).