Same difference, they went with 2/4 rather than the much better 2/5. Either way, the sabertooth board is the only one of the two capable of running two of their upcoming flagships (595 ARES) at x16, since that looks to be a three-slot as well. Poor decision imo.
They all look identical and the article says any slot is capable of running at x16. To me, this gives you more options for where to put your cards over the sabertooth unless I am missing something obvious here.
You can run GPUs in slots 2 and 6 with a sound card in the pci (slot 5)
or put two three slots cards into spots 2 and 6
or put a pci-e x1 card in slot 3 and run GPUs in slots 4 and 7...
tl;dr I don't think you can tell if the board has any prefered 2x16 configuration just by examining the picture as all the pci-e slots look similar.