They used to be good about matching offers, but as of late not so much. Not sure why, as its just another nail in their coffin as more and more people flock to Chase (who will match better offers within 103 days of opening the card)...
For me (and many others), Chase has better transfer partners, thus UR points are worth more than MR points. And thenAmex shut down their shopping portal, and as the icing, my interactions with AMEX CS have been overwhelmingly negative. They need to step up as Chase is really pulling ahead of AMEX, esp for premium cards.
Amex does match, but unlike Chase, they don't have a written policy in which they strictly adhere to. Chase will always match within 90 days without exception; conversly, Amex does it on a "case by case" scenario and entirely at their discretion, though I have no idea how they determine it.
I agree that in general, the UR program is better for those who fly UA, and also because UR points have a 1 cp redemption value without restriction. However, MR would be better for those who don't value UA, and only use MRs FF partners.
Regarding the shopping portal, I don't think it's a big loss for the MR program. There are way better options with evreward, topcashback, and all the other airline specific shopping portals. Many Amex users often use their cards on UR and shopdiscover anyway, and most times get the portal points. The only thing I find better with the proprietary portals has mainly been groupon at 15% (now 10), and the seasonal specials on UR (such as 8X for Brooksbrothers, sears, gcs, etc...).
Called up Amex today and the CSR rep said she thinks they will be able to apply it to me! She said it had to be sent over to the customer rewards department to find out for sure but I am hopeful. 100,000 MR points would be fantastic especially since I was originally only going to get 25k