I've been in about 60 countries. After a while the novelty/new perspective feeling diminishes. I don't really think it's worth the effort to see all countries. What's a country anyway? Mostly borders. People and cultures are a different thing and tend to spread differently over borders.
I agree. For example take Mexico: one country with many cultures. You can't spend a weekend or even a year in Puerto Vallarta and say you've been to "Mexico".
Having also travelled extensively, people ask where 'home' is. While 'home' might be where the majority of my family is, I can honestly say "earth". Maybe that's an uninteresting answer but it's really true as I have no interest whatsoever in space travel.
I came to post the exact same sentiment - why all the obsession with countries and not, say every climatic zone, or every major language group or every integer latitude, or whatever.
I agree. But I think countries can be a useful proxy if they aren't all, say, Western European, or Carribean.
The big culture zones IMHO are
Americas: North, Central, South and Carribbean;
Africa: Southern, Western, Eastern, Northern;
Europe: Western, Mediterranean, Eastern;
Asia: Middle East, India, South-East, China, Central, Japan/Korea;
Pacific: Islands.
Obviously personal perspective will divide or agglomerate those, but its a rough guide.