I think the COD effect will eventually wear out, the problem with EA's approach of trying to cannibalize COD's userbase with Medal of Honor is that they're always going to play second fiddle, but in turn MOH has basically lost its own identity.
Uncharted 2's MP is, surprisingly, still averaging 50k per night, obviously not COD numbers but actually it's pretty darn good after more than a year, I think the approach is to build a strong brand that has its own share of the market and grow it with marketing and critical acclaim, as well as strong community features and play modes that will provide longevity.
It's not an impossible task, I wouldn't have believed if someone told me that COD would overtake HALO as the online shooter brand this generation but it happened, I don't expect U3 to be THAT big but concentrating on establishing their own brand of gameplay is far more viable. When the COD formula is no longer hip, EA will be left holding the bag having to remake the MOH brand, AGAIN.