I think - when you saved your Pages documents in Tiger (in the newest version of Pages), there is an option in the Save sheet to "Include preview in document". This, obviously, was in anticipation of QuickLook in Leopard. I am assuming that none of your documents (either because they were created with Pages 1.0/2.0 or you hadn't enabled the saving of previews in the save sheet of Pages 3.0) therefore contain document previews in the document bundle.
Possibly you just need to resave your documents - with the "Include preview in document" option checked, though in Leopard this may just be done by default upon saving in Pages?