Meaning: "shit happens, but it was so obvious that this particular shit would have happened that whaddaya gonna do ?" Taken from the upcoming Samuel L. Jackson movie of the same name, and immortalized by screenwriter Josh Friedman on his blog post of Wednesday, August 17, 2005. It is a rhetorical phrase, and entirely unneeded, like "I told you so".
It is "snakes on a plane" that a movie with the title "Snakes on a Plane" would eventually be filmed, and of course that Samuel L. Jackson would play the lead role (a perfect match). Not surprisingly, this film will be a huge box office success.