Just caught this off the Ausiello blog on ew.com: Calista Flockhart scales back Brothers and Sisters workload
What I found interesting is that the Aussielo states that this was a contributing factor to Robe Lowe leaving the show, since he had already begun to feel his role was diminishing. This just sealed the deal. It makes sense, given that Flockhart plays his spouse, and although she will remain a regular, being in less episodes means less focus on all aspects of her character. Without her, what reason would they have to see her husband? On the flipside, you can refer to the Roseanne factor, in which the husbands and boyfriends appeared more than the daughters, which kind of felt a little odd, but somehow they made it work. Maybe Lowe should have given it a shot.