...So why didn't they use them in earlier OS's?
I'm not challenging, I'm just curious
Probably because they couldn't, mainstream computers weren't powerful enough yet, or the ideas just hadn't been developed into reality yet. For example, Microsoft has been batting around this Surfaces interface concept for a few years now.
Just like the idea of a completely seamless integration of home PC, handheld/laptop and work PC (plus any other devices you can think of) that intelligently and instantly transfer whatever you're working on or have open from whatever device you were using last to whatever device you're currently using.
For example, if I'm reading a news article at home and have to get going, I just get up and walk away. During my commute I turn on my handheld and, boom there's the article automatically pulled up. If I start writing an email on my handheld and get to work, I turn on my computer and, boom, there's the email I'm writing right there when I turn on my work PC.
It was an impressive presentation a couple years ago, but the technology has a little catching up to do.