Read the license associated with the icons and just make sure commercial distribution is permitted, if it isn’t you can contact the author and ask for permission that way. My experience with contacting most authors with this kind of stuff has been pretty good. Most of them don’t really care how you use them but they just want you to ask and maybe credit them in some way.
I’ve been basically using the honor system but I may be looking into a way to better protect the files.
I also have a custom 404 error page on my server that will automatically shoot me an email when people are looking for something that isn’t there on my server. Twice I have gotten several 404 errors from person (not a search engine) that was trying to access quite a few of the images on a theme but spelled a few wrong. It was enough attempts that I blocked their IP address for 48 hours from my server just to be safe.
The 5% that don’t have JS either available to them or turned on are not the crowd I want to market to. Plus, they do have JS available to them. They can go upgrade their browser or system like the rest of the world.
What this comes down to is opinion. An author has a choice not to support IE 6 or other browsers if they choose and yet they are still given the opportunity to make money for their work. JS is the same. If they choose not to support degrading JS, that is their choice and they should still have the opportunity to make money for their work.
You have to keep in mind too that a lot of the authors here are new to building web templates and are learning as they go. That doesn’t mean that they shouldn’t be allowed to make a profit off a functional template just because their JS doesn’t degrade.
Just my 2 cents.