In a post, earlier in this thread, I did agree that Apple stores have a tendency to have a lot of people in them at any given time. I don't disagree with you there. I was getting at the fact that they are going to be extra crowded after an iPhone launch. Annoyingly so.
Honestly, I hardly ever buy accessories at the Apple store. You can get the same stuff much, much cheaper via Amazon. Most accessories are over priced at the Apple retail stores, just as they are at Best Buy and the carrier stores. There is a lot of profit to be made selling those cables and cases. The few times that I have bought such items at an Apple Store, it was because I needed the item on the spot. Don't remember items being out of stock with what I need, but I trust you when you say they were with what you were looking for at the time.
Regarding technical support and repairs, I guess it's a case of experiences may vary. With a couple exceptions, I have always been treated well. I once went in with an old Macbook that was over a year and a half out of warranty to get the battery looked out. It needed to be replaced. The rep gave me a new one and didn't even charge for it. Said don't worry about it, this time. I'm aware that's not normal, but it did make my day and helped frame my overall opinion of them.