The 360 has 2x songs and 'more popular songs' for Pro upgrades. The question becomes is the PS3 audience for 2x songs significant in comparison. I would expect to see at least one person complain about being 'forced' to buy songs again and/or complain about the 'cluttered' library. There may also be a complaint about how 2x is only available for Expert.
However, it doesn't seem too far fetched to believe that 2x will have a higher level of interest on the PS3 than Pro guitar. Most drummers have the drums so they just need a pedal. Pro guitar requires that extra purchase, period.