This blog post is funny. Not so much for the humor, but for the sheer inaccuracy.
Absent a member # and an expiration date (or an indicator of being a Life or EPL member), it's not a "membership card." Pay up and they put you on the rolls. Otherwise, you've been solicited as a potential member, but you're not one.
As for why the NRA isn't going to the Great Obama Gun Control Summit, you have to ask? Really? If a fire hydrant is in the way of where you want to park your car, do you think it'll move if you step out of the car and incessantly bang your head against it? No. Same applies to NRA, Obama and Gun Control.
The NRA has finite resources in terms of both time and money. Why burn either on a pointless exercise when the real work to be done is in Congress, in the State legislatures and at the grass roots level? The NRA doesn't have to resort to astroturfing, unlike some other activist organizations. They actually have real work to do.