The numbered route tree, and play calling based off a numbered route tree, is a Don Coryell technique*, passed on to people like Joe Gibbs and Norv Turner. The advantage of using a tree is the speed with which you can teach the offense to a newcomer. So it is often associated with what Dr Z called the "real West Coast offense", those teams that use Coryell's principles in their passing game.
A Coryell style offense will feature timing routes, a deep to shallow QB read, a go for the throat passing mentality. Think of the Rams teams that Mike Martz coached for, or for that matter, the early 1990s Dallas Cowboys.
But ABQCOWBOY is entirely right, there isn't just one passing tree. Further, stealing successful pass patterns is as old as football.
These days, I'd say it's not about the specific route, it's about the pass play as a whole, how the patterns piece together to make it close to indefensible.
A good introduction to a modern passing offense are Chris' Brown's articles on Peyton Manning's offense:
http://www.grantland.com/story/_/id...n-manning-indy-offense-ignited-denver-broncos
http://smartfootball.com/offense/peyton-manning-and-tom-moores-indianapolis-colts-offense
* I'm saying technique because I'm sure someone numbered routes before Coryell. Coryell then used the numbered routes to describe plays. A '678' would be the X running a 6 route, Y running a 7, and Z running a 8. The simplicity of the play calling greatly eased learning his system.
