If you buy the game two months late, thats on the player. At launch, there should be an even playing field for everyone. Someone shouldn't have to be obligated to play the beta so that they'll have an even playing field when the game goes live. A lot of people don't want to play betas because they're often buggy, exploitable and are generally an unfinished product. That said, playing the beta and knowing the quickest way to do things and where to go is often more than enough advantage.
I also hate the 'there should be a reward' thing. I can understand Bungie wanting to give players something as a thank you, but to actually expect it as if you deserve it is beyond me. I've said it on Reddit and I'll say it again here, there is a bit of entitlement there.