Just because you're exceptional doesn't mean you're a superhero. A background of a couple of years of thievery doesn't turn you invisible.
Not so... or at least not any more. In AD&D 2E, what you wrote was true, but in 3.5 edition, commoners are at least level 1 too - see the NPC classes (these classes are weaker than PC classes though) section of the rules.
If we're going to say "any more," then perhaps we should speak of 4E? Where it's even more true.