Rosenfeld attributes the drop to economic weakness, high unemployment among young adults and aggressive pricing by both Mondelez and category leader Wrigley.
In May Microsoft effectively stopped treating Live like an add-on for a videogame console and started pricing the console as a loss leader for an entertainment platform.
Scottish Liberal Democrat leader Willie Rennie has also come round to the idea of minimum pricing, which the SNP previously wanted to set at 45p per unit.