By accident I forgot to put any ranks into Balance and was still able to take SWF & iSWF. I didn't noticed until I couldn't take gSWF. The character has a Balance Tome+5. I confirmed it by testing with a new iconic. Tried to take SWF at L1 and could not (no Balance ranks and no Balance tome). Ate a Balance+2 tome and was able to take SWF at L3 with zero ranks in Balance.
Was this an intended change to the feat that never made the patch notes? Has it always been that way and I never noticed because I believed the wiki?
It potentially nets another 5 skill points. So, not a big thing -- will likely end up in a "fluff" skill like swimming.