I think it's possible to agree with both sides here!
I agree that children ought to be taught to move out of the way - it's not something they know automatically and most of us want to bring up people who know how to be polite. You do this by getting them to move when they are in the way. But it isn't a total obligation, every single time - there will be times when an adult needs to move out of the way for a child. And they should equally be polite enough to know it. A child who assumes they are always more important than an adult is obnoxious. So is an adult who assumes they are always the most important one present.
In a supermarket, a child wandering around should move out of the way of an adult. At a Punch and Judy show, put on for kids, the adults should move out of the way to ensure the children can see (lady in the fluffy jumper thing, standing up in the second row, I am glaring at you...).
Surely it's all about the situation, not a general "I am more valuable than you are and you need to get out of my way". In the situation described in the op, I'd be asking dd to get out of the way (she's 3). I do also expect that if she doesn't then the adult who wants to pass will ask her - she's still learning this stuff and doesn't always get it right. I really don't get what the problem was with this - why on earth wouldn't you ask, instead of assuming that 'This is what is wrong with the Youth of Today'? I may not always move my offspring the precise second you think I should - I might not have noticed - I don't walk around on full alert every second of the day and I don't mind someone else stepping in if what I am doing is keeping only half an eye on her while I think 'Crap. Forgot the shopping list. What was I supposed to be getting?'
If a child does move out of the way, do you say thank you, as you would to another adult? Or do you take it as your right? Because if the latter, then you are really not practising what you preach in this whole 'respect' debate, and you are exactly the sort of person that I don't want my child turning into - a rude, entitled individual. I find it ironic that my child would have to defer to you in order to learn not to become you! (Can I just say I used 'you' not directed at anyone, but because using 'one' sounds ridiculous. I'm not accusing or targeting anyone.)
This debate seems to have become polarised. It isn't a choice between either making kids into second class citizens, in a world where the adults are always right, or turning them into little brats. It is perfectly possbile to bring up polite, well mannered children, while still acknowledging that they are people too, with the same rights as everyone else. This is what the vast majority of posters are saying - not that children shouldn't be taught manners, but they they do not automatically become subservient to adults in every situation. Everyone should be considerate towards everyone else, and that includes adults being considerate towards children.