The problem with the best settings out of the box is they can never cater for the non-standard use of email ports for downloads by some p2p programs and probably shouldn't try.
So it is as RejZoR said a compatibility issue with programs not conforming to standards rather than try to configure avast for regular usage. Exclusions in this case to my mind are not a configuration tool but a conflict resolution tool.
So, until avast's mail scanner started responding to non standard use of the email ports the p2p user would have been none the wiser about the non-standard use of his out of the box settings of his chosen p2p program
So, this out of the box is a double edged sword and program writers should conform to internet standards (where they exist) in their default settings and out of the box experience.