But I would say in the 'post mainframe era,' we've gone from a time when most computers were mainframes to a time when most computers are not. Thus talking about the 'post pc era,' implies (in my opinion) that the vast majority of people will only have a table.

Surely that would be when the vast majority of computers are not PCs, not that the vast majority of people only have a tablet. Given the ubiquity of devices in the average home that have microprocessors, that do computing jobs that PCs can do, that aren't actually PCs, we've been there for a while.

Now if he'd said that we were in the tablet era, that's another thing.