eyeinthesky, in general I agree with much of your post.
I hope by now that people understand why my first reply in this thread was so vehement - largely because, as professionals who (almost universally) take a pride in the way they do their work, object to being told things like "You must follow ATC instructions". If, however, I was OTT, I apologise.
A couple of points on your post, eye.
No, forgetting something is not like forgetting to level off at cleared altitude. The vast majority of modern aircraft nowadays have flight directors which will command the level-off at the cleared altitude. This system will fail for a variety of possible reasons - e.g., the altitude was mis-set, or was mis-heard, or QNH or 1013 was not set, etc. etc. In a fairly long aviation career, quite a significant bit of it as Flight Safety Officer for a couple of organisations, I have never heard of a level bust resulting from forgetting to level off.
Next, I have never said that pilots are incapable of remembering an instruction for 30 seconds. I said that pilots (and everyone else) are capable of forgetting something told them 30 seconds ago. There is rather a big difference. And at a busy phase of flight, when you may be slowing down, configuring the aircraft, possibly rebriefing the approach, waiting for the cabin secure signal, talking to handling agents because of a late request for a wheelchair, checking the new ATIS because it's just changed, sometimes we forget things. Yes, there are two of us up there. But quite often only one is listening to you.
Yes, I appreciate that this is an important question for you. I have never said it wasn't, or that it was anything but important to any pilot who takes his job seriously and takes a pride in it.
But, occasionally, sh!t happens. And when it does, it's no good complaining about lazy pilots, or deaf pilots, or talking to them as if they were children who don't understand how hard-working, stressed, heroic ATCOs are working their butts off for a bunch of ingrates who don't appreciate them.
I know how hard you guys work. I've seen it. (I've even tried it - thanks, MAN). I don't know how you do it. But don't for one moment imagine that we sit up there all the time with our feet up waiting for the next cup of coffee saying to ourselves "ATC want what? S*d 'em. I can't be bothered."
As I've said time and again, we're all on the same team. Take the time to appreciate what goes on the other side of the ether. Do you know, I've never once had an ATCO in the jump seat?