Well, they have. But not necessarily for the worse. Here are the new T&Cs for OfficeMax:
Automatically get up to a 10% discount OR up to 4 additional Membership Rewards® points for each dollar spent on eligible purchases at OfficeMax®.com
Get rewarded on office supplies, ink and toner, furniture, technology products and more. Use your Business Card from American Express OPEN on eligible purchases at OfficeMax.com and automatically get a 5% discount credited to your American Express statement or get 2 additional Membership Rewards points on every dollar spent of $250 or less and 10% or 4 additional points on every dollar spent more than $250.
So. More options are usually better, but I'd have a pretty hard time choosing 4 MR points over 10% cashback. That's valuing the MR points at 2.5CPP, which is about a penny too high in my estimation. I haven't figured out how to "choose" the cashback yet, but I've sent in a Secure Message to find out. I'll update this post with the answer.
I received a response to my SM. Here's the relevant portion:
It looks like Amex is changing things up a bit with cashback remaining the default. Bonus MR points are bound to be better for their bottom line than cash discounts, so we'll see how long that lasts. At least the discounts aren't going away just yet. Losing them would be a serious blow to the Amex business program.