Was just looking at the TEN HD TV Guide on Channel 10's site and it seems there will be 2 episodes of Smallville on 17 January! One at 7.30pm as usual and then another after at 8.30pm.
Not sure why this is happening, but it could be due to the episode at 8.30pm having a more mature content of sorts, possibly. Either way.. great news! :)
More like Ten just filling a time slot and would expect this to happen more often with the writers strike catching up to most regular TV series now in the US.
Plus with season six being released in March I would say it is the end of Smallville in Oz on free to air, Foxtel may continue carrying it again later