You are right Scott, on some sites there is a robots.txt editor, however my site doesn't have one and I can't figure out how to get it to show up.
I created one manually and it still doesn't show up the Edit Files tab of the Yoast plugin. I had another Robots plugin installed that perhaps commandeered that part of WP or something...?
I also get this entry in the .htaccess portion of the Edit Files page:
“If your .htaccess file were writable, we could do this automatically, but it isn’t so these are the mod_rewrite rules you should have in your .htaccess file.” Then in the box it says, "Options +SymlinksIfOwnerMatch"
My site is old enough I was running Yoast's plugin back before it had the Robots/HTAccess integration I believe also, when he had the separate Robots Meta plugin...
Yoast if you get time, I'm sure you have dealt with these issues before so link us up to some details for the resolution(s) if you can! Thanks!