Play game, want fun, has fun - SE gets the money, good game. Doesn't really matter what you're doing so long as it's upholding value on both sides. And the whole deserve argument sort of falls off because the game has already decided what they deserve and therefore it decided they "deserved" that achievement.

Smash 10 kupo nuts, get Thal's Nut Crusher. Doesn't matter if it's easier 6 months after content release, smash 10 kupo nuts and you get the reward.

So... as long as they didn't cheat they deserved it. They are correct in being entitled to the reward, as they did what was necessary.