In reply to Ciaran Whelan.

Not having it would actually be a bonus for WP. See, plain, run-of-the-mill PHP is part of the reason WP is so easy to get into. There's no special templating engine. It's just HTML mixed with PHP. That makes it easy for new theme authors to get into and Average Joe to modify.

The docs would be only be available at a handful of places that are specific to either WP or a particular templating engine. I'd consider that a disadvantage. Basic PHP + HTML is documented everywhere.