Why? There's a whole kingdom of really bizzare life, called Archae.
Also, the notion that prokarya are simple and uncomplex is totally bunk. There's a whole genus of prokarya - actinomycetes - that have such a complex lifecycle, and stage through single-celled spores, and multicellular superstructured colonies, that for many many years, scientists thought they were fungi.
"Simple" is quantifiable as how much information-theoretic complexity a population's selection pressure can sustain against mutational entropy to allow for relatively permanent (on non-evolutionary time scales) adaptations. It's not a measure of how much an organism makes us say "Gee whiz!" This is what I was referring to.
