Personally, I felt there wasn't much difference between the normal and ultra versions in regards to water retention (ie, both will make you retain water). The ultra product does work better, but you still won't see just how well it worked til a few days after you've stopped using the product and the water retention ends. As long as you realize the water retention happens but goes away, everything is fine. Its annoying in one sense, but cool when you see a very noticeable change at the end too when you've "dried out."
So to answer your question, not everybody gets a diuretic effect from the caffeine.