Uncomplex is probably the wrong word. Averagely complex for this sort of thing? Not easy to achieve or trivial to build, but, from a 40,000 foot perspective, probably typical of the kinds of complexity you'd find in most popular web applications.

There's a very long discussion, somewhere, of Amazon's eventually-consistent architecture that I'd say is definitely on the high-complexity side of things. Unfortunately I can't find the link I'm thinking of, at the moment.