For what it's worth Dell does sell several configurations of most models that ship immediately or next day. Personally, I prefer to build my own, but I help my clients choose Dell PCs from time to time and it's never been an issue getting them delivered within a week. If you look for "Smart Selection" or "Quick Ship" models, you'll find quite a lot.

Apple works the same way, in my experience. When I ordered my Air a couple years ago, I couldn't buy it in store because it was a configuration they didn't carry and it took several days after my online order before it even shipped from China.