>>1
The big thing about UNIX and Unix-like systems is the insistence on decomposing the entire system into small components with a lightweight interface. You can contrast this with IBM (or to a lesser extent, Windows) systems where programmability requires interfacing with a large, inflexible framework of some kind. On UNIX, you just reach into the guts and pull out what you need. Some people will emphasize text orientation as a major component of this, but it's really just the way interaction is typically enabled.
>>4,5
Yup. The big evolution is that you can easily yank text around both the shell and the editor to mung and re-execute. There's no more struggling with screen or the X clipboard to move text somewhere for a one-off job. All your interaction with the system is still defined by the text, but you now have less friction involved in designating what text to use.