Joe Donato commented on Destiny is suffering from the same problems that plague MMOs:
My reasoning is that getting to level 30 is a goal and repeating the Vault of Glass and weekly events is an activity I find enjoyable. The Vault of Glass is still really exciting and challenging (no one in my group cares to cheese it). Eventually I'll want to get through the hard raid, and after that I'll be 30, I'll have everything I could need, and there's no reason to keep going.
At that point it's all good though. I can go play other games and hope that Bungie makes valuable content for my level 30 character going forward.
You're right in the sense that there's no good reason to get to 30, as you can do the hard raid at 29 and 29 doesn't require raid gear. I'm just going in with the assumption that, like most things in Destiny, more purpose and value will be built in over time.