Hey applets could manipulate JavaScript data/the DOM. There is a bit of bark to the 'Java script' bite. It was very slow, though, sending through the JVM process and to the browser process each time you read or wrote a value (and the plugin that did this I think was in its own process - memory is hazy there).

Overall it's hard to say how Sun could have won here, perhaps acquiring macromedia and using Flash technology to make a browser that ran those cool portals out of the box, and hey scripted first-class in Java too btw ;-)