I've long held to the theory that digital sales have much better legs than physical. I've also called people out before for claiming sales of a game to be 30%+ digital first week and the like. Clearly that wasn't the case here (on console at least where physical is actually relevant). The 30%+ digital figures companies give out are for lifetime sales, it makes sense to me that the digital % would start out quite a bit lower than that and build up through a games lifetime and these sales seem to support that theory.
PC having better legs also makes sense to me, although I've always thought that would be more noticeable over the longer term. The majority of yearly sales being on PC within 3 years is a bit of a surprise. My reason for thinking PC would have better legs over the long term has been due to the permanence of the platform other consoles. I wonder if used game sales could potentially explain why PC has taken the yearly sales lead so early?
Used salescould also explain why digital has longer legs.