For those that think that a slightly lower WS should not be allowed to hit on a 4+, I think it's worth remembering that in the 40k universe, there is no such thing as a fair fight. Combatants use every trick in the book to kill their opponents. It isn't sparring, it isn't a game [to them], it's life and death.
This whole thing got me thinking about a rather well known movie... I've made some slides up to briefly outline the scene.
To set the scene, our hero isn't a particularly well trained fighter. He's more of an academic, and he's run afoul of a trained killer...
As we can see, our hero is sorely outmatched and will surely be killed, as he's nowhere near the calibre of fighter that his opponent is. In fact, the Swordmaster is so sure of his victory that he's showing off for the crowd, taunting his victim, yet our hero seems unperturbed...
We suddenly realize why he's unmoved, when he pulls a superior piece of equipment from his holster, and shoots the Swordmaster...
Although the Swordmaster is vastly superior in skill, and in a "fair" fight he'd have minced our hero, our hero's no fool, and the Swordmaster is no match for modern technology...
So what's this got to do with anything? Glad you asked! The current system takes into account how relatively easy it is to shoot someone at less than 20 yards, or lob a grenade in front of them and wait for it to blow up. The scenarios outlined by those suggesting alterations to the existing "To Hit" chart seem to think that close combat is fought hand to hand. As a Guard player, I'll tell you that if I saw any manner of monster / alien / super human charging at me with a giant chainsaw, I wouldn't be preparing to receive the charge with a knife in my hand... I'd be laying out the firepower faster than I could think, and that's what the existing "To Hit" chart recognizes. It's really easy to shoot someone that's trying to stick you with a sharp object... and that's an observable, historical fact. Ask the Incas. Well trained warriors that were sorely lacking in Kevlar vests.