I'd assume that behind the scenes the models generate several passes and only show the user the best one, that would be smart, as to to make it seem their model is better than others

Is also pretty obvious that the models have some built in prompt system rules that makes the final output a certain style. They seem very consistent

It also looks like 40 has the temperature turned way down, to ensure max adherence, while midjourney etc seem to have higher temperature.more interesting end results, flourishing, complex Materials and backgrounds

Also what's with 4o's sepia tones. Post editing in the gen workflows?

I don't believe any of these just generate the image though, there's likely several steps in each workflows to present the final images outputted to the user in the absolute best light.