Mercule
Adventurer
It's fine, even logical, for it to be rare. But it needs to be viable.Not many people want to play a character that doesn't have good synergies with its class abilities. How many rogue players would play a rogue with a Dexterity of 14 in 4e? And if they did, even I would call them silly for doing so. But maybe the rogue has everything the player wants, but he wants to base his character around Wisdom and not Strength or Dexterity or Charisma because that's not how he envisages the character.
In 3e, I played an acrobatic rogue (dilettante son of a wealthy merchant who did a lot of base jumping type of stuff). He had a 14 dex and 16 str. He was a blast, pretty heroic, and fit the rogue class perfectly. I would object, quite strongly, to any system in which he was a "silly" character.
Probably also worth noting: other than a brief stint with a barbarian, that rogue was the strongest character in the group. (Ironically, the main fighter was a dex-based duelist which made for a wicked team-up.) One of the things that turned me off most in 4e was the ability score escalation. 16 should be a pretty respectable stat.