According to http://caniuse.com/script-defer, most browsers support the script tag\'s defer attribute.
I would like to know if scripts spec
The defer attribute has a good write-up and analysis. Also See the comments to the post for additional info on how defer has been re-defined in HTML5.
My conclusion: defer is too browser dependent to count on. Therefore use the jQuery doc ready technique.
To put it another way, an important reason for jQuery is to cover browser inconsistencies. Defer is another such inconsistency that should be avoided for well written pages.