The default behaviour of javadoc is to only generate documentation for classes, interfaces, and members that have protected or public scope. Use the -private option to generate documentation for everything. Other options are -package, -protected (the default) or -public. Just type javadoc with no parameters for a full list of options.
I use javadoc comments for all classes, interfaces, and members, regardless of scope - because I think its good style. Not sure what
you should submit to Sun though - I suspect the default behaviour is probably most appropriate because it only details what clients of your API can get at.
Hope this helps.