American Express Membership Rewards - Membership Rewards - Tiers

Does anyone know what tiers are in the membership rewards program?

I had an email today from AmEx telling me that when I got my Platinum card last year (I already had a Corp Card and a Rebate Card) that I was wrongly placed in the "Basic Tier" but that they have now corrected it and put me in the "First Tier".

All I know is that they said there is no price difference (with regards to the $75 fee to link my Corp Card).

There are three tiers. Most the free cards get a MR express program that can't be redeemed for airline miles. The basic level can do airlines. The MR First program adds some super high-priced rewards, mostly for things I can't imagine redeeming for.

See http://www.flyertalk.com/forum/showthread.php?t=706374&highlight=tiers for details.