This is a wank argument that stupid people always use to justify unoriginal music. Think about it - yes there are 12 notes but western music gave us extremely limited ways of using them. The 12 tone system makes better use of the tonal range but is arguably even more limited than that. Even so, in a 2 minute song, you only have 12 notes, but those notes exist in multiple octaves; you have in addition infinite ways of using them either together as chords or sequentially, infinite note length rhythmic combinations, infinite structural possibilities and infinite dynamic and instrumental combinations. That leaves essentially zero room for ripping stuff off.