Yes, you're right it can't be truly random, but as good as really... But anyway, your theory relies on the pedestrians being always moving, but in gta3 and vc the peds are only loaded when they're near you. Otherwise, they don't move.
My method that i'm developing works by removing control of peds from the game tottally, and "out sourcing" it to my program. This has been mostly successful... Just need to work on the more complex stuff (such as actors following paths in reverse and interacting)...
eAi