A look at the sordid history of these numbers reveals just how useless they really are. To begin with they appear to have been extrapolated from the results of a survey compiled in the 1980s. The survey was conducted on a small sample of US businesses, with the resulting numbers then multiplied into an estimate of worldwide losses not from piracy, but from the IP laws in many countries, which are far less restrictive than in the US.
And even its authors apparently didn't have much faith in their figures, noting that they "could admittedly be biased and self-serving." Not exactly a glowing recommendation to take it seriously two decades later.
Although this doesn't bring us any closer to real figures, it does reveal something that may be more important. If there is any real evidence compiled since this study it's less compelling. Otherwise we wouldn't keep hearing the same old story.