Current skin kill forums, as that is x6-x12 bigger in size /for each page need 500K of traffic without graphics (comparision to 2.3.x version it was around 50kb)/ ...
need lightweight, but fully functional skin availability for perpetual license holders

The initial page load would be bigger, but the CSS and javascript would be cached, and each subsequent page load would be SMALLER than IPB 2.3 (because of the better and lighter HTML structure). In the long run after a couple of page loads, you would use less bandwidth with IPB 3 over IPB 2 on the same given page using the default skins.