From the OpenSolaris forums, by way of Daring Fireball's John Gruber comes word this afternoon that Apple's decision to remove ZFS support from Snow Leopard was based on licensing issues.

Specifically, Apple may have wanted a "private license" from Sun Microsystems, and Sun simply did not want to play ball. Neither side could agree on suitable terms, so support was removed. [OpenSolaris Mailing List via Daring Fireball]