Random is random. It's funny - people complained that the Apple shuffle algorithm wasn't working, as sometimes they would hear the same song very close together. They had to massage the random to make it not truly random, and weight it so songs wouldn't be chosen that close together.
The user spotlight isn't picking from all of the 10K+ members; you have to have posted within the last 60 days, and visited within the past 30 days, so it's a somewhat more compact set of people.