While I agree with your point about the current Leeds love-in probably being something to do with the fact that most of their success was within living memory (i'm in my thirties, but even I remember them playing Champions League football), statistics like the list above don't tell the full story: Leeds were only founded in 1919, by which point some of the teams on that list (including us/Wednesday) had already spent 20+ seasons in the top flight. In fact, Leeds have probably spent more seasons at the top level since 1919 than we have...
Forest I can't explain though