Todd,
The quizzes are always randomly generated. So if you take a 20-question quiz on integration, then the simulator will select 20 random questions and present them to you. It disregards the "% per domain" because only the Integration Knowledge Area has processes in all five domains. So if -- for example -- you took a quiz on Schedule Management, the system COULD NOT give you any questions in Initiating, Executing and Closing, simply because Schedule Management is not involved in these 3 domains.
However, the full, 200-question exams #1 - #7 are fully aligned with the exam content outline. Each exam will present the appropriate Domain % to you based on real exam conditions.
So in short: Quizzes are random and Exams are fully aligned.