With standard Vaadin components I do not expect to see that kind of UIDLs either. Standard Vaadin components really use very little data to render since they mostly deal with text. In those cases the UIDL is probably somewhere between 50kB-100kB at best.
However, when you start using graphing components (like the MandelBrot addon in the demo or the Vaadin Timeline for instance) then you will see those kinds of UIDLs since they usually are very data intensive and a lot of information needs to be transmitted.