For you it's some silly invisible number but have you ever actually fired a gun? You don't shoot straight the first time you fire it or even for quite a while after that. The more proficient you get the straighter you shoot. That's what the skill represents. Would you really expect someone who just walked out of a peaceful vault and had only ever shot a BB gun before to be able to hit the broad side of a barn with no instruction or practice?
What's the point in having a role playing game if you can't roleplay? If this was a game designed solely as a shooter sure it would make sense to have the main character be a marksman, but this is a game designed so that you can do what you want whether its LEARN how to shoot a gun properly or to just go around chucking grenades at everything that moves or to not hurt a fly. If the past games are anything to go by you don't start out being a gun toting killer. The skill is there to represent your character learning and progressing. Borderlands is an RPG in the sense that you can roleplay this type of killer or that type of killer, it's not really a roleplaying game, it's a shooter pure and simple. Every single one of the characters in borderlands revolves around shooting things, there's the sniper, heavy gunner, mechanic, and healer archetypes but they are all essentially guns for hire. You have no choice but to shoot everything that comes your way. Fallout's different in that if you want to you can just sit around town blowing your money on poker or sit in a strip joint or hunt animals or just wander the desert avoiding the enemies (from past game experience obviously) Sure things might still try and kill you but that's life in a post apocalyptic wasteland. If you want to be able to shoot up the desert then put a little time into it and get proficient at it and then have at it. Meanwhile those of us who don't want to fire a gun will find that if they pick one up they aren't gonna be able to hit jack with it. And that's how it should be. Excluding the insane vaults like the boomers I doubt most of them have much in the way of fire power or a reason to use it. It's only once you get out that you start having a reason to use combat skills, the vaults aren't military installations training killers (for the most part) so it makes sense that you can't just shoot straight without having picked up a gun before. Hell if anything I think they should make you have to really look at a gun (and have sufficient intelligence) to figure out the safety and magazine release and whatnot the first time you pick up a gun or have it taught to you by someone before you can go around shooting or changing the magazines.