When exporting a wrapper there are two options, Export With Wrapper and Export Without Wrapper; the later setting to be used when your style hasn't used any custom wrapper changes (IE it uses the default wrapper).
When you import a style that comes with a wrapper, it simply gets added to your list of wrappers; whereas if you where to set your style to use the default wrapper and select "Export Without Wrapper" you wouldn't bump into these issues (basically authors need to only send a wrapper with their style when they've made changes to it, otherwise they should opt to export without the wrapper).
I'd take and open the styles you DO use and see if they will work with the default wrapper and select that for them to use, then delete any others that are lingering.
As for the style chooser, it should list any styles marked as "active", so go to the style editor and make sure the only items selected are valid themes that you'd like to have displayed.
