Yes, I also wondered about those stats a few days ago.
Anyway, the answer is that the statistics are simply wrong. Either they used different settings for those 2 versions, or they are taken from a different time period, or something else - but the detection capabilities of avast! Home and avast! Professional are the same.
Btw, shadowserver.org uses linux version of avast! scanner, neither avast! Home or Professional - where the detection capabilities might be slightly lower than avast! Home/Pro, due to some missing unpackers (though they are gradually approaching the Windows version).