Back then all that stuff was basically low-hanging fruit. The time was right. If Xerox hadn't come up with them, someone else would have within a couple of years.
Also, they were all conceptually pretty simple.
Believe it or not, running an app store is massively more complex than any of those things you listed. Dealing with payments across countries, legal entities, fraud, security, hiring processes, employee performance standards, and so forth. A laser printer or a GUI is much simpler in comparison.
Also, that terminal emulator you're describing -- first, it's not just an emulator, it's adding a lot of new features. Second, developer salaries have skyrocketed relative to inflation. So even accounting for inflation, $12M goes a lot less far than it did in the 1970's.