When I read this I was thinking, "Yah, that's how I am sometimes!" but also feel that it's a push to be more competitive/ effective as a healer. And what if both healers were expecting the other healer to pick up the low HP person.. then you get the 'OMGWHYDIDN'TIGETAHEAL!?'. As a tank I would appreciate more seeing BOTH healers blowing CDs on me to keep me alive. That would encourage my trust in them more to know that all my healers have good reaction time.
I tend to find the 'trying to do too much' less of a problem and more of a positive trait. I mean.. why be bored as a healer if the DPS always gets to go 'balls to the walls' and the tanks are always swinging away for threat generation. Hopefully you'd never see a tank ignoring adds swinging at the clothies just because 'ohhh I assumed the other tank would pick them up so i didn't do anything'. And by then all the clothies are dead. And mad. >:(
So if all the others get to have excitement and be able to push themselves to the limit, why shouldn't the healers ? :D

Also remember you don't always have a pally in the raid, or a disc priest or a druid. I've seen 25 mans without a priest or without a druid. And especially in ten mans, The shaman MAY very well have been brought to Tank Heal. No class alone can be said to only be able to heal one specific thing in one way. We all get a whole plethora of abilities that allow us to be good healers in many different situations; you just have to understand how to utilize and apply those abilities.