OS X does not behave exactly in this manner, but is indeed confusing.

Linux never needs a 'purge' or equivalent. Doing a 'drop_cache' only slows the system slightly because nothing is cached. 'sudo purge' can prevent OS X from using swap – i.e. running out of RAM even though there is RAM it could reclaim. This behavior has been tweaked but not fixed in Mavericks.

Actually, purge is completely unrelated to swap. Purge forces disk cache to be flushed to disk, and can be used to approximate a cold disk buffer cache scenario for performance analysis.

Some small amount of swap usage (compared to total RAM) is perfectly normal, by the way. More cache, for instance, is a better use of RAM than avoiding swap usage by keeping never-accessed pages present.