Sorc/Summoner knife cuts both ways guys...and it goes on over all classes, not just casters.
Summoners often bid on items obviously of more efficient use to Sorcs and therein lies the issue as well.
Personally, I choose to never bid/roll on an item that has pet focus as i do see it aimed at summoners. If there is a summoner in raid, it is of benefit to the entire raid that he be the one to utilize the benefits of the item.
The couple items i own that contain pet focus were taken because there was not a summoner present at the time.
If your leadership lacks the sack or simply doesn't care enough to regulate who may bid on an item, simply use your own heads and police yourselves. Speak up in vent: "I'm gonna pass on item X; it's definitely of better use to a summoner/sorceror/chanter". A few people doing this regularly will influence everyone and it will take on a life of its own throughout your raid. This works for all classes; tanks, scouts, heals, etc...
What helps each individual player helps the whole raid. There is nothing OP in a raid setting as far as I'm concerned as it is helping me and my fellow raiders regardless of who's topping the parses. It's a team sport.
-Din