What you said is true. It's just that they've hit the critical mass.

What is Pokemon's slogan?
"Gotta catch 'em all"

As I said, the last game I completed the dex on was Pearl and it was hard enough as is. Collecting all 493 Pokemon actually became very tedious but I wanted to be able to say I've done it on at least one game. I can't see how anyone could bother at all with these new ones. They must have what, nearly 700 Pokemon now?