At first glance, both ranged and close-combat have their benefits. The main benefit that I really see with ranged is exactly that, the range, as you are now able to have a greater threat range, meaning that you can take units out from afar. However, I do not wish to dispute the statement that close-combat is where most of the damage is caused, and in this conclusion, I shall be quickly skimming over why I believe this is the case.
Firstly, I believe that the number of attacks is a big issue here. In assault you can get a huge number of attacks off. If we look at a comparison with my Orks. 30 slugga boyz on the charge get a whopping 120 attacks altogether for 180pts, whereas 12 lootas – again, 180pts – can only churn out a maximum of 36. So lets look at the mathammer for this against a bog standard 10 man tactical squad. Tactical squad gets 11 attacks (inc sergeant) hits with 6 (being generous today), and wounds with 3. 3 Orks are killed, reducing the number of attacks against the marines to 108, of which, 54 hit, 27 wounds, and 9 marines are killed. Ouch. Now for the Lootas, 36 shots, 12 hits, 10 wounds, 3 marines die. About a third of the damage that the boyz caused. Now I know that you could argue that Lootas should generally be popping transports rather than taking shots at marines and that Orks are at heart a close-combat army anyway. But this principle that a dedicated close-combat unit from a codex causes more damage than a dedicated shooting unit from the same codex for the same points follows in most instances, the exceptions being Imperial Guard and Tau.
Secondly, the availability of the ability to cancel out army saves is much more prevailant in close-combat than it is in range. Looking at dedicated close-combat units, a large majority of them have access to some form of power weapon or rending, just off the top of my head I can name Bloodletters, Genestealers, Nobz, Assault Terminators even Lychguard, whereas how many ranged squads can have access to AP1 or 2 weapons/rending weapons at the same proportion as these do power weapons. Space Marine Scouts can get a lot of snipers, Deathmarks, Chaos Chosen. I mean sure, many units can get access to things like plasma weaponary but in what quantity can they get it. Imperial Guard Veteran squads can only get plasma for 3 of their 10 men, Eldar Guardians can only get 1 Starcannon platform per squad. The sheer quantity of hits that cancel out armour saves in close-combat is horrendous when compared with that of ranged, and when coupled with the weight of attacks seen above, this makes one brutal combination.
Third and finally in this brief summation of ranged vs assualt. One reason that assault kills more in my view is the potential to hit multiple units at a time. Only a couple of units can hit more than 1 target at range in a single player turn, Long Fangs, Land Raiders and super heavy vehicles in apocalypse spring to mind here, but in combat, any unit can multi-assault, and when they do, they can cause utter devastation. Just last month when I was playing black templars my 1 of my squads of Nobz (with the standard warboss) ate a Land Raider, 2 tactical squads and an assault squad due to catching them in a multi-assault, killing 4 units in a single game turn, whereas the potential for a standard unit specialised at ranged combat is to only kill a single unit per turn.
And so close-combat, with it's additional attacks, inclusion of a large number of armour ignoring weaponary, and the ability to hit more than one unit at a time, makes it much more devastating when it hits than range. However, don't rule out range altogether, as it is necessary in a good list to be able to threaten units at distance, and if you don't have this, then you're in trouble, and if Imperial Guard and psyfleman dreads have taught us anything, range can still cause a heck of a lot of damage.