Even the old dog did it:

In 1999, Slackware saw its version jump from 4 to 7. Slackware version numbers were lagging behind other distributions, and this led many users to believe it was out of date even though the bundled software versions were similar. Volkerding made the decision to bump the version as a marketing effort to show that Slackware was as up-to-date as other Linux distributions, many of which had release numbers of 6 at the time. He chose 7, estimating that most other distributions would soon be at this release number.