kohlrak: Depends on how they track that data. The easiest way to track the data would require self-reporting from user (unlikely) or self-reporting from steam (very likely).
And i'm willing to bet steam is not going to separate online purchases vs online key redeems. So, just for example, the majority of games were sold as steam versions on disk (like Skyrim), they'll count as both physical and digital copies, and then 2 or 3 people bought online exclusively, it'd look like a 50-50 split with slight majority of people leaning towards digital. Now, if you look at things from a realistic perspective, and knowing that with all the talk of piracy back then, i'm willing to bet the steam key redeems became fashion back then. I wouldn't know for sure, though, since I was too busy playing my old copies of older games with my sub-par computer and focusing on console titles otherwise.
EDIT: And wasn't that about the time of minecraft as well?
I'm pretty sure they do.. I remember some games I bought physical that came with Steam were listed as retail key in Steam. I'm not going to debate it though, according all availble public information which you can Google the vast majority of PC sales are digital. So I'll leave it to you to look it all up. :P