On the Gog.com Homepage I can see the best selling games of all genre's.
Also on the gog cataguelogue I can sort on bestsellers, But now my question is:

Why show the list on the homepage shows (sort on bestsellers) other games then the sorted catalogue on bestsellers? Even If you don't include the "free" games on the catalogue.

On main page are "temporary" bestsellers.
In catalogue you see bestsellers during much much longer period of time.

I was also wondering, thanks for this answer. Would anyone have a more precise definition of the time span for these two charts?

I'm guessing the one from the catalogue is an all-time one, but what about the one on the main page?

At the moment it is set like from last DnD promo so I could say "last month"?