Predicting this in the 70s? No big deal. It wasn't hard to foresee by then if you're anyone with modest knowledge of technology. If he'd predicted it in the 50's or earlier, then I'd be damn impressed, steadily more the further back the years go from there.
A modest knowledge of technology in the 70s did not embue the vision outlined by Clarke, I give him a bit more credit. I'm sure most people from that era would be astounded by where we are today.
I mean, someone from the 70s would definitely be surprised by the specific technologies we have (and don't have). I don't think they'd be surprised to learn that every person has a personal computer (of some type) or that technology has become so ingrained into our culture.
It was pretty clear back then that computing and electronics were on a very fast trajectory to more or less where we ended up.
I only did a cursory search, but seems like by 1970, IBM was worth nearly a billion dollars. It was a pretty safe bet.
