The Hebrew alphabet is actually an abjad rather than a "true" Western-style alphabet, in that every letter represents a consonant, and vowels, if they're indicated at all, require diacritics.
This leads to uncertainties in how to pronounce words. Why did G-d use an abjad rather than an alphabet in which to give us the Torah?
An academic reason would be that indeed Hebrew (and other related languages) don't need vowels for disambiguation as much as, say, English. Most Hebrew words are built out of triliteral consonantal roots, so that words with the same consonants are (usually) related, differing only in how they're inflected for different parts of speech, number, tense and so forth. Contrast with English, where the vowels play a much more important part in the etymology of words, and taking them out indeed causes a great deal of ambiguity (which is why "disemvoweling" is effective for trollish comments).
Also, classical Hebrew has a CV(C) syllable structure, meaning that a word can't begin with a vowel sound. (Most Jews don't pronounce the letter א, but properly speaking, it is supposed to be a glottal stop.) By contrast, an English syllable can begin with anywhere from zero to three consonants, so there's much greater potential for confusion.
A more classical Jewish approach, as YDK pointed out, is that this very ambiguity allows us to derive multiple layers of meaning from the written text. In the case of G-d's name mentioned in the original (linked and closed) question, it can in fact be written with many different sets of vowel signs, each of which symbolizes some particular way in which He relates to us and we to Him. In other cases, details of Jewish law or thought are arrived at by contrasting the way in which a word is actually vocalized (called in the Talmud mikra) with other possible ways that the same series of consonants could be pronounced (called masores).
Rabbeinu Bachye on "lo sechanem" (Vaeschanan, 7:2) gives multiple ways of reading the prohibition based on fiddling with the vowels. He gives this flexibility for multiple versions as the reason for the Torah not including vowels. See R. Bachye also Behaalos'cha 11:15.
