Amare should have been suspended, no doubt. He seemed to be heading towards the altercation in a very bad mood.
Diaw broke the rule too, so he should have been suspended, but to me it seems like he was really interested in checking on Nash and I thought he caught himself (unlike Amare who had to be physically pushed back).
I think they should have been suspended because the rule is in place, has been since they were kids (aka they grew up with this rule in place in the NBA), they were reminded of it more than once this season, the it's been consistently and harshly enforced since its inception.
I agree the rule is a bit unfair and needs to have a little wiggle room, as well as a more properly defined "immediate vicinity of the bench." However, the NBA did the right thing is suspending them. You have to enforce the rules you have, period.
No doubt it sucks. I'd be pissed off about it if the roles were reversed, but I'd be pissed at the players who broke the rule.