That's the Relativist Fallacy.
Just because you don't see them in the same light as other powers does not mean they are not powers according to the rules. (p287)
And if the proficiency bonus didn't apply to powers, they'd not apply to basic attacks, which would mean ze goggles, zey do nozzing.
Fortunately, the bonus says 'attacking with' and that means using any power's attack that uses the weapon as your Weapon accessory. Where you'd not get the bonus is in cases where the weapon doubles as an implement (Swordmages are the easiest example, Wizards and staffs are a second, Pact blades for warlocks a third) for Implement accessory powers.
The key is the Keyword. Weapon means you apply the proficiency bonus of the weapon to the attack, Implement means you do not. (caveat: Commander's Strike does not attack with your weapon and therefore does not grant -your- proficiency bonus to the attack)
As an aside, not only is vanilla a flavor, they did research on perfumes and found that men find vanilla to be one of the most enticing scents to put on a woman. Vanilla is -definately- a flavor.