Apple's purchase experience is an incredibly personal one. I grab a blue-shirted employee and tell him/her what I want. They either bring it. Alternatively, they hand you off to someone. The fact that they can charge you using a handheld (without a checkout line or counter) startled me the first time I experienced it. I was also surprised that they could email receipts. This contrasts with my experience in Duane Reade or Sears where buying gum forces you to deal with 3 feet of paper. These are the positives.
Sometimes their experience sucks. It is still better than other places. 1) Employees are chatty even when there are other people waiting. 2) When employees "go up" to get your stuff, it takes a long time. A couple of times, I've wondered if they ran out of the Kool-Aid that makes them smile so much and are getting their refill :-p
Your post said you liked gas stations and Ikea. I agree that gas stations give you a quick self-service experience. Ikea, on the other hand, is on my hate-list. It is damn near impossible to find an employee in the stores I've visited. Self-service in retail is an interesting idea. It works great for simple transactions. I've seen it fail miserably at airports and grocery stores.
I'd say my experiences at Apple Retail Stores have generally been positive but have been inconsistent and certainly has room for improvement. I don't like how the checkout location sometimes varies (back, front, handheld) but I admit overall, Apple does it better still than most retailers.
Obviously it's not killing them (!), but I do think they need to clean up this part of what's an otherwise really good experience.