You mean like if you were playing 1e, and you switched to 2e, your half-orc assassin or a monk were out of luck?My opinion is simple. If you were running a 3rd edition game with just the core books and then decided to switch to 4th edition, the new game isn't complete if you can't accommodate all of the characters in the campaign. If you happened to be running a half orc barbarian or a gnome bard, I guess you're out of luck.
I guess 2e wasn't complete either.