@Hershel -- team bonuses are force multipliers; damage bonuses are additive. But damage bonuses with big numbers on them (which certainly includes Superior weapons) are the easiest way to get something to multiply.
A ranger armed with war axes is going to be making 4-6 attacks a round (more in a burst round) in most rounds of a combat, at least once you hit high heroic. So that +2 damage from the bastard swords turns into 8, 12, or more damage a round (or 24 damage minimum in epic, where all your attacks are 2W or better)
More, many striker strategies involve crit optimization at some point -- a ranger with multiple attacks, an Avenger (or multiclassing into Avenger) for a few rounds of double rolls, bards handing out automatic crits -- et cetera. And superior weapons have a -big- advantage in crit optimization, as few CO strategies don't involve gaining High Crit at some point--and high crit is both easier to get with superior weapons like war axes and fullblades (although there is greataxe; one of the best martial weapons in the game if you can get +hit somewhere else) and sets its effectiveness based on the weapon damage die. In paragon, a war axe with Deadly Axe is doing an additional 13 damage per crit, plus another 4 damage per W vs a longsword--so about 25 extra damage per crit on encoutner attacks, and 17 on at wills.
Regarding that avenger--well, the crit optimization is even stronger there. And any extra damage the Avenger does is going to be force multiplied to the nines, both on the multi-attacks (hammer of the forge, Fury's Advance) the Avenger pretty much automatically takes if they want to be an effective striker, and on being handed extra attacks (or free crits) by the leader.