You can talk to people and buy items in lots of games. Zelda set up the gameplay style for others to refine, that were never any question about genre. Tomb Raider was built off the formula. Beyond Good and Evil totally refined the formula. There's plenty of others. All considered either action, adventure, or action-adventure games. The fact that you can save your game (especially these days) or buff out your character with new/better items and/or more health means nothing. And NPCs are common in almost all genres now.
I think most people want to believe its an RPG because it's kinda slow and set in a fantasy setting.