It's true that FedEx is one of the most expensive LTL carriers to ship with. But they offer money-back guarantees along with bundled Ground & Express parcel discounts and so they land alot of big, national accounts. This means greater density, which is key to profitability in LTL (and parcel).
No offense to OD and other pure-play LTL carriers, but it is becoming increasingly difficult to compete against FedEx on national accounts - especially with the growth of core-carrier relationships. This is why UPS had to buy Overnite because FedEx was hurting them with bundled LTL\parcel discounting. And it is why DHL will have to buy an LTL carrier if they want to compete against UPS and FedEx.
The surcharge cut means that for every $1000 a shipper puts on Fedex trucks, they will save $50.00. Doesn't sound like much but since FedEx deals with alot of big customers that ship often, it does add up.