From having played both basketball and soccer, and having reffed basketball, I'd have to say there are some interesting differences. And I think they all have something to do with the restrictive size of the basketball court.
Simply because there are so many bodies in such a small area, you will have more contact than on a soccer field. So there are more incidents that need to be judged. At some point it becomes necessary to more formally divide the responsibility.
Because of the constant proximity of the players, a good basketball team continuously screens and cuts to get players open and the defense is constantly moving around screens and switching. There is so much going on all the time in a basketball game. I have never seen that much off ball action in soccer. Perhaps that's because I never played above high school?
There is also a different tradition, and thus perception of making calls "in front of your partner" in basketball. Many coaches know the officials' areas and get quite upset if they know you're calling out of your area. And it's not always just trying to play you off your partner. If a coach sees his players getting hammered off-ball and sees that both of you are watching on-ball, he's got a legitimate gripe.
Then there is the consistency issue. If you've been calling contact in your area consistently, and your partner occassionally reaches in and grabs something that you've been passing on all night, it ruins your consistency.
And as others have cited, the NBA and the NCAA have both conducted studies that show a large percentage of calls outside an official's primary are incorrect. Much of that, I believe, stems from not seeing the whole play develop. You can get in a lot of trouble if you're making calls on plays you've only seen part of.
But everything I have mentioned is a generality. Some games and teams don't generate near the amount of contact or activity. Partners do get screened out or lose angles on plays. Things do happen in partner's areas away from the ball. Occassionally a partner suffers vapor lock on a must-get play right in front of him. Stuff happens.
Any well designed set of hard and fast rules about calling in or out of an area will likely be right most of the time, and wrong some of the time. So I tend to take a progressive approach to calling outside my area:
- If it happens any where in my area, it's my call. I want to be the one to make it.
- If it happens in the gray area, and there is any doubt as to whether my partner saw it, I will call it.
- If it happens in the key, and there is any doubt as to whether my partner saw it, I may call it.
- If it happens away from the ball in my partner's area, I might call it.
- If it happens on-ball in my partner's area, I won't call it unless somebody loses a limb and it is completely obvious that my partner couldn't see it happen.
So other than traditional double-coverage areas (the gray area, the key), the farther it is into my partner's area it is, the less likely I am to call it. The closer to being on-ball it is in my partner's area, the less likely I am to call it. If it's on-ball in my partner's area, I am extremely unlikely to call it.
But there are some exceptions to those generalities as well. Curl plays going to the basket and away from my partner, I'll help if I clearly see a foul on the back side or from a secondary defender. A block/charge call involving a secondary defender I'll help with. Pass and crashes, we're supposed to divide coverage irrespective of areas.
Then there are times when you need to expand your area into your partner's to help out. When lead goes out wide, trail has lead's post. When the lead's area is empty, he expands to cover off-ball in trail's area. There are probably others too.
And lastly none of that matters if there are things of interest to be watched in my own area, which is normally the case, because I'll be watching that. So normally I'm not watching my partner's area. Sometimes I do see into my partner's area. Occassionally I should be looking into my partner's area.
Two-person basketball mechanics is everlastingly a game of intelligent trade-offs. You cannot be successful by staying in your area every moment. And IMHO any official who says "never fish in my pond" doesn't understand two-person mechanics. And IMHO any official who doesn't understand that going out of your area is risky equally misunderstands two-person.