Why Have Some of My Widgets Disappeared After Switching Launchers?
The widgets referred to in the question are TouchWiz-specific widgets. They will only show up in TouchWiz because they don't use the standard Android widget interface. I've found some references to Samsung releasing a TouchWiz SDK to develop such widgets, but those articles are from 2009 and the links they contain now lead to Samsung's developer home page, rather than to a specific page. I've also seen references to some of the widgets being ported to work on any Android phone, but I can't confirm as XDA seems to be down at the moment.