I honestly think that post 6u10 things have gotten so much better on the applet front, that that should be the preferable method to show the innocent bystander. Especially 4K where we don’t need native libs, and there is not really a need to specify a JRE version.
For anything serious I’d pick Webstart for deployment (if I could either pick applets or webstart) for numerous reasons, like not losing your user when he clicks [prev] or presses F5 after the applet lost focus, and for the simple reason that while the Java Plugin might be finally stable now, the browsers themselves are littered with bugs, which affect applets.
If the goal is to promote J4K among non-Java folks, applets might be the best option, because it feels just like Flash: embedded in a webpage, no JavaWebstart GUI with a progressbar.
I’m in no position to state whether the goal of J4K is to promote Java games, and I can imagine that ‘the next guy’ can point out some very compelling reasons to pick Webstart, in which case it would have been a mistake to restrict deployment to applets.