To find out why Whizzy causes the problem I'd suggest talking to the people behind the editor and see if they have any suggestions how to fix it. I've never used it so I can't really say.
One way to get around the problem is to tell your editors that instead of the lazy normal single quote they have to use the typographic single quote (on my Mac keyboard itís shift+alt+'). However in order for it to work across the board you would do well to set the db collation to utf8_general_ci or utf8_unicode_ci per Keyrocks' suggestion earlier, as well as making sure that all your snews files (index.php, snews.php) are using the UTF-8 charset setting AND that UTF-8 is set as the charset in your Admin panel -> Settings ->Time/Locale. I do this all the time on my own sites. I understand that it may not be entirely easy to get people to do that, at least not if they're used to typing the standard single quotemark, but it would most likely help. Of course you'd have to try it in Whizzywig first to make sure it actually works.
Another approach might be to change to a different editor, TinyMCE for example. I can't say for sure if it would help with the single quotemark problem, but it might. I have a couple of clients where I've used TinyMCE as the editor in sNews and none of them have reported any problems of this nature. Last resort could be to go with the default sNews editor and tell the editors how to use the various buttons to get the basic HTML right.