Also companies never like to tell exactly how many videos they reproduce/sell--it makes negotiating the lowest price with the talent more difficult, if the performers can figure out exactly how many of their videos were sold last time. In fact, when performers leave and sue their former company, it's often because they have discovered "real" revenue numbers--that means they were entitled to bonuses. (This also happens in the mainstream movie biz.)
With all this in mind, most industry executives will declare a sexvid a "hit" if it sells 10,000 copies or more. Of course, this number gets "messy" because some of these "sold" copies (to retailers who sell it to me and you) are returned after, say, six months of sitting on the shelf.
Bottom line: the big companies (that can get a bounce from softer versions of their product on cable) sell more than sexvids that don't make some sales to a more mainstream audience.
And, lest we forget, all dvd sales numbers are becoming more and more "moot" due to the advent of the internet VOD, and the performer's personal website.
In fact, in the interview currently on-line with AVN, Vivid's boss, Steve Hirsch, says his company is now making more money from internet related revenue than from sales of dvds. Which explains why production companies (Vivid, Club Jenna, Digital Playground) also try to control their Contract Stars' websites as part of their signing deal.
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