Quick question about blank referer.

Excuse my n00bishness, but can you tell me why it is that affiliate managers don't get suspicious when they see tons of 'no referer' clicks. Don't they look at it and say to themselves, "Why the hell are so many people either typing in this guys affiliate url or have it bookmarked?"

Do you have to mix it up with lots of traffic w/ referer or is blanking referer becoming common practice to prevent aff managers from stealing ideas and methods? Or do you just keep the amount of clicks to each program reasonable and under their radar.

Thanks