The high-pitched tones of some of the characters are there to serve the story. They are there to emphasize the childlike qualities and innocence (or, in some cases, contrast the innocent sound with evil intent) of the characters. No, most Japanese people in real life do not have high, squeaky voices. Again, this is simply to serve the story and not to represent real life accurately. I will elaborate.
First, I’m assuming you mean how the original voice actors speak, and not whether the American voice actors dubbing the film are recreating how the Japanese version sounded. The Americans aren’t. Their jobs are to create believable characters in English.
So are the words Japanese voice actors are saying true representations of conversation in Japanese? In some ways, yes. In some ways, no.
The tones and general word choice have to be relatively realistic so that the Japanese audience can allow themselves to be drawn (no pun intended) into the world of the story. The audience has to accept the characters and their interactions as plausible before they would be willing to accept the story they’re enacting.
But there are many things that are exaggerated. For example, Japanese (and all other countries’ voice actors, for that matter) overemphasize their diction. They pronounce every word clearly and try not to drop sounds. To use an English example, many people “swallow” the t sound at the end of words—for example, don’t becomes don’, but voice actors always pronounce the t distinctly. The Japanese do the same. Voice actors try to pronounce words as distinct units without letting them run together. This is because everyone needs to understand the words they are saying. If you are conversing with someone one-on-one, you or your partner can stop the conversation and ask for clarification of a word or phrase that wasn’t understood. TV and movies can’t stop. So the voice actors must make sure that their words are easily understood the first time.
Also the scripts are written so the audience can differentiate characters easily. So in anime, female characters use the sentence-ending particle “wa” more often than in daily life. Young, tough characters will use an exaggerated speaking style using “nee” for every “nai” they say. Intelligent characters use words that even intelligent people in real life don’t say, and rich people are completely overblown. But these things are accepted by the Japanese audience because very little time is reserved for introduction of these characters, so you need the cliché words to define these (usually minor) characters quickly.
If you’re trying to learn Japanese from anime, it isn’t too bad a venue since the diction they use will make their words more clear and distinct than non-actors. You can also pick up on the rhythm of Japanese sentences, and a lot of vocabulary words you learn watching anime are very helpful to you in real life.
However, you should always realize that the dialog is not originally intended for you to study to. It is there to serve a story, and not to demonstrate Japanese for you. So take the voice actors’ turns of phrase with great skepticism as you learn from them.