I use Transmit (on the Mac) for FTP. It has an option to set the permissions on upload. I suspect other FTP programs do this as well.
What’s interesting is that I just did a ‘touch’ and the file was created with 644 permissions.
As a DreamHost user, your account is created as its own group as well. Every FTP user in my account belong to my own group. Having files as a 664 would let all of your accounts modify this file, but not everybody else.