Is anyone really enlightened? Or is it just some meaningless bullshit term from a primitive religious people who lived several thousand years ago?
It's certainly a goal worth striving for, knowing full on that you'll never get there completely, much like many of lifes more invigorating pursuits I'd imagine.
As far as Watts was concerned I've listened to and read quite a bit of his material. If I had to make a guess as to why the end of his life ended up so different than that of his sober beginnings it would be his relentless philosophical practices.
Philosophy without restraint will drive a man to drink I know this from personal experience. If you're familiar with the psychological phenomonen known as 'existential crisis' you should be plainly aware that regardless of how disciplined in the techniques of zen buddhism, one who builds his life's work on the practice of continually questioning the nature of reality will invariably result in a prolific body of work lined with very real sometimes frightening insights, but will likely self-implode in the process.
Ask Lenny Bruce, Bill Hicks, Andy Kaufman, etc. about it if you should ever get the chance. Philosophizing for a living is not something that I woudl ever figure to end well.
I think it's not a matter of practicing what you preach. More a matter of your discoveries eventually overcoming your practice, and since we're dealing with mortal men here the practicioner gets old, worn out, the practice suffers, the drink or something similar becomes necessary, and then it's simply a matter of time.
I'm guessing on intuition that he wasn't a charleton. Just another great mind that burnt itself out for a greater, collective good.