The Races & Classes book says "We've also tied barbarians and druids closer together, creating a relationship between them similar to the link between paladins and clerics."
This in no ways implies that they would have the same ROLES. Perhaps Mike Mearls is refering to the fact that they both use the Primal source, or that their fluff connects them.
He also goes on to say "We also wanted the barbarian to be more than a fighter who rages" which COULD mean that a barbarian would suit another role better (like the striker).
The book also says that druids will be less spellcasters and more shapeshifters, which MIGHT not make them leaders.
While I'm not saying I know for sure I'm right, (far from it!) I think it's a bit overstating your omniscience to be so sure I'm wrong, Lackhand.
Fitz