There is a big difference between mailing lists and web forums. Most mailing lists are not moderated, whereas most web forums are. Most web forums are not archived, whereas most mailing lists are. Most mailing lists are plain text, whereas most web forums use some kind of markup language, usually an annoying one that's slightly different than all the other markup languages out there.
When you host something on an FTP server, it's usually because you have some relationship with the admins of that server. You can't get binaries up on ftp.kernel.org without talking to the kernel.org people. Whereas if you use megaupload or one of the thousand other file lockers, all it proves is that you know how to wait 15 seconds and click through some HTML forms.
I realize there are exceptions to these generalizations-- for example, the lwn.net web forum is one. Google+ seems to be another bright spot in the sea of mediocre web 2.0 walled gardens. But in general, there is a reason why mailing lists and ftp are preferred.