Adelaide and Port never play hame games on the same weekend. Apart from showdowns, its always one at home and one travelling. I think a strict home-away-home-away rotation applies for all non-Vic sides. Only Melbourne, North, Dogs and very rarely Geelong travel twice in a row; not counting finals. (Richmond may have done once.)
An SA club playing in Melbourne/Adelaide for two consecutive weeks does happen now and then. See Rounds 18 and 19 this year.
Round 18
Adelaide v. Carlton - AAMI Stadium
St.Kilda v Port Adelaide - Telstra Dome
Round 19
Adelaide v Richmond - AAMI Stadium
Carlton v Port Adelaide - Telstra Dome
It's the WA sides that stick to alternating home and away due to the distance.