This has happened to me a lot in the US when I was carrying my harp, but the cynical side of me said it had more to do with being an attractive female than anything else (judging by who offered the help!) 
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This happened to me constantly in the US. As I said, practically evey week when I did my grocery shopping.
I am a petite woman and probably look more fragile than I am.
I look the same in the UK as in the US, though.
It's a common ploy in supermarkets and other shops to keep moving things around, presumably to get the customers to pick up something they wouldn't have otherwise while looking for their intended quarry. 
Yes!
I have lived in the UK for 6 years and have shopped at the same Morrisons weekly for the vast majority of that time.
Items are constantly being moved around.
I’ve had workers wander around looking for things when I’ve asked them where something was because they didn’t know.
while people are sometimes a bit un-self-aware, I've never found them to be rude
What do you consider to be the difference between being un-self-aware and being rude?
I’ve certainly never had anyone intentionally push me hard, shout at me, insult me, etc.
What about the couple who stand in front of the shelf having a conversation while people behind them are trying to get things?
What about the queue jumper who doesn’t check to see if anyone else was waiting before them and assumes they are first?
What about the guy I saw this weekend casually strolling around the aisles while listening to his ipod?
What about the woman who let her daughter ride her scooter down the aisles till the daughter fell and started crying? (Happened the week before.)
When does un-self-aware become rude?
I think that being polite, by definition, means being aware of, and considerate of, other people.
Don't worry - it's not really that bad. You'll be fine! 
Definitely. I wouldn’t even have thought about it if it wasn’t for this thread. You will get used to the way things are done.
I’ve certainly never had any confrontations with people, just been annoyed.
I was much more annoyed when I first moved here. Now I am used to things and would probably not be used to a US supermarket.