FreeBSD only appears to use more swap than Linux. In actual fact, it does not. The main difference between FreeBSD and Linux in this regard is that FreeBSD will proactively move entirely idle, unused pages of main memory into swap in order to make more main memory available for active use. Linux tends to only move pages to swap as a last resort. The perceived heavier use of swap is balanced by the more efficient use of main memory.
Note that while FreeBSD is proactive in this regard, it does not arbitrarily decide to swap pages when the system is truely idle. Thus you will not find your system all paged out when you get up in the morning after leaving it idle overnight.