A unit points cost is based as much on the units stats as it is on the units usefulness to the army or the formation it is part of.
Also.....
Straight line crossing of stats from WH40k to Epic-A can, and does, lead to problems. Sometimes it is more important that the proper Army Wide Feel be created over a direct crossing of said stats form WH40k to Epic-A.
For example, not all Space Marine Devastators in WH40k are armed with Missile Launchers, but they are in Epic-A, why? Because it creates a simplier, easier to use, cleaner game then trying to allow for all the possible options they do have in WH40k. Also, it really isn't that important that the individual stats be that detailed, this is a BIG PICTURE game compared to WH40k and in that case the overall effect of a weapon system is often more important then the individual effects it might, or might not, have on a unit by unit bases.
Deathspitters, Bolters, Lasguns, Shuriken Catapults, are all treated as small arms in Epic-A no matter what their WH40k stats are. They can cause a change in FF to hit, or number of FF attacks, but not become a ranged weapon.
Raveners, at various times, have been tried with +1 attacks, while it seems real correct the overall effect has always been bad, either upping the cost so much they become near useless, or making them so powerful for the cost as to be a no brainer (Thus leaving the Gaunts at home).
The desire is to create the feel of a wall of nasty little bugs that won't go away no matter how many you cut down, that are backed up by bigger meaner bugs that can be gotten rid of if you could just catch your breath long enough to accomplish it. Hence you want cheap Gaunts/Ravaners/Gargoyles so this effect is created. The need to do this in Epic-A will sometimes supercede the need to stay in line with WH40k.
Well that's my two cents anyways.....
Jaldon
?I really do have one my friend's girl gave me ... could explain a lot of my recent problems ! 
