Why is it so bad that xF does a little bit of QA and active involvement in the RM? Again, they are providing this service for free for any author, and setting some rules to follow is not a bad idea. Just to slap on some warnings on addons based on certain criterias, like xF version they are released for, author's last login date etc. And as SchmitzIT pointed out, xF is now in the unique possision where it hasn't been much changes over the last year, so allot of old resources are still working, however this does not have to be true going forward.
I also agree with Mike, that a certain level of professionalism has to be expected when submitting resources, especially paid ones.