I believe one commenter on the post made a good point:
"Photostream is design to protect your pictures using iCloud. Those that look at Photostream as a management tool are stretching it beyond its intentions. Photostream only accounts for the last 1000 pictures on iOS but on a Mac there's no functional limit.
Once you realize that Photostream is more of a lightweight protection service it becomes more clear why it needs to be separate from your camera roll."