I'd say the advice is spot on for someone new to the industry. If you are new, or trying to break through, or even going from tgp/ll/or some other variant and looking to take the next step to a paysite, the advice is good. Stick to what you know.
But.. if you have been in thr industry for sometime, then you probably have picked up enough knowledge of what sells, marketing, promotion, and different interests that you can sell anything. I would personally think that the tip comes from keeping your interest more. I know for me, I would not approach a tranny, gay, midget, ass, tit site with the same enthusiasm as a foot fetish site. So for me, keeping in my interest makes my work more enjoyable.
