Where is your data coming from? The World or the US? The only way I can see 40% PC still being boxed is pretty much Blizzard titles... you can't even find retail boxed in stores anymore outside of a few titles. They must also not be including quite a few of the DD outlets.. retail for the PC hardly exists at all.. at least in the US.
I still see plenty of PC boxed copies at Target/Walmart/etc. A lot less than console, but they're still there. Most of the bigger games get boxed copies. Blizzard stuff, Valve stuff, Civilization, Sim City, Skyrim, etc. Hell, I think I've even seen games like Torchlight and Peggle on a shelf somewhere.