These are really two entirely different topics. Connected realms serves Blizzard's perception about the needs for a viable realm size. Cross-realm zones serve several purposes. The two big things are Blizzard's perception of what a zone should look like in terms of its at-the-moment population and another desire on Blizzard's part to consolidate their network resources so they aren't running several hundred nearly empty versions of individual zones.
Connected realms are very good things. I'm agnostic on CRZ because despite everyone else's horror stories it hasn't affected me in any noticeable way (other than a slight bump on boundaries) and when I talk to real-life in-game friends about it they mostly report the same thing. So no opinion there other than I if I have to level a toon I like to see the occasional person on the way from level 1 to end game. There have been times when I've probably seen less than a dozen people all the way from one to 80 and that's just wrong. CRZ may or may not be the best answer for that but having an entire zone to yourself in an MMO is unacceptable.
Anyway, back to the beginning: zones and realms are different things with different requirements.