It’s good enough for the style of American English adopted as a concession to typewriter limitations, since that’s pretty much exactly what ASCII is designed to support. OTOH, American English as used outside of that context doesn’t use straight quotes, but rounded ones in each direction with different meaning, uses various diacritical marks, and also uses the cent sign (¢), the obelisk (†), diesis (‡), pilcrow (¶), section sign (§), division sign (÷), multiplication sign (×), less-(and greater-)than-or-equals sign (≤ and ≥), angle brackets (⟨ and ⟩, which aren’t the same as less-than/greater-than symbols), the interrobang (‽), and—the next three distinct from the hyphen—the minus sign, en-dash, and em-dash.
> See the fact that most Americans have never installed a separate keyboard layout.
Common software used for text, like MS-Word, provides convenience methods for many non-ASCII characters without an keyboard layout change.