Well, in real life a 700 mph merge is a lot harder to aim for. You don't have a little tracking thingy showing you were to line up a half mile out, you only have this little speck of a relection that suddenly becomes an enemy coming right at you. This is a compromise needed for an online arena.
And I think that because of the "way things work" in AH2 it's an awful lot easier to dump a huge burst of ammo in front of someone coming at you than to get hits in a proper tracking shot. Not that the gunnery model is necessarily wrong, but with a head-on you don't have to worry about warp delays (or ballistics or lead) where you would in a tracking shot. And that's where it starts to get technically artificial.
And, of course, your reason is just as valid. If you can gut-shoot someone 10 times better than you and get the kill half the time, why not? If you miss you can replane and try again in 5 minutes.
But, let me ask this hypothetical to really stir the pot: if head-on fighter kills were treated like manouever kills ... that is no perks ... would people do it as much?