[Japo]

That's the question, b and β are different realizations of the same letter, that is we consider them the same sound and don't distinguish words by them. w (sounds just like u, except that w is followed by another vowel in the same syllable) is even more different from v than English w in what and b in bat. I think Russians and Dutch people tend to mix up English w and v and most can't quite pronounce either completely well, but in Spanish there's even no v, v is pronounced b. Also vowels can be realized short or long and it's the same word, unlike in English for example bitch and beach.

In Spanish there are fewer functional different sounds than letters in the Latin alphabet, and there aren't two that are not very clearly distinguishable. Even if there can be variations that language scientists classify as different, we consider close ones the same letter, and most Spanish speakers aren't conscious of the difference. There are only five vowels--long or short are the same; English in comparison has dozens of different vocalic sounds, that may be the only different between two unrelated words.