Apple released a version 6 for Lion when Mountain Lion can out that mirrored each other. Since then Apple as moved toward version numbers being tied to a particular OS and .x updates to mirror later OSes.
Safari 7 with Mavericks - Safari 6.1 (or 6.2) for ML and Lion
Safari 8 with Yosemite - Safari 7.1 for Mavericks
I think we'll see a Safari 7.2 and maybe Safari 7.3, but Apple sucks at updating old Software. Unless you plan to upgrade OS X you'll eventually want to switch to Chrome or FireFox to get the latest technology.