By now the sales certainly look more like a trend than a spike. Theorizing:
Software sales should be an indicator for what people are playing. Considering that the 360 has had about 50% software market share (counting wii/ps2/ps3/360) the last 2 month this should mean that the 360 has been generating more word of mouth and try-before-buy opportunities than the other consoles, and this may be contributing to the sales trend.







