Mustrum_Ridcully
Legend
The system actually does that. As long as you have a striker in the party it doesn't matter what kind of flavor it has. All that counts are the mechanics.
Of course you can reflavor 3E classes too - but those, especially prestige classes, are usually build with a theme in mind, not a function. In 4E, the function comes first and foremost. It is even clearly stated that they made sure your character will function in its role no matter what you do. So, it really doesn't matter if you call your striker a warlock or rogue or ranger, or what mechanics you use for any of the three, as long as it's a striker.
Flavor is irrelevant for the mechanics - which is also seen by the lack of "antimagic field" and similar things that may only affect one sort of powers.
Is seems as if we are talking cross-purpose.
You are right, it doesn't matter what kind of Striker you play for the purpose of defeating encounters. But each individual power is still themed after what kind of Striker you are.