When (and IF) Fluenz does a complete upgrade on Italian, you won't be charged extra for it. At least, that was the case when they did an upgrade on Spanish.

This question comes up periodically, about one language or another, and the answer is always the same: it's a function of regionalism. Speakers in one part of a country pronounce certain words differently from how they're pronounced in other parts. (I remember when I lived in Berlin, I was surprised to hear the soft "sh" sound when I was expecting the more guttural "ch" sound.) Think about English -- whether in America, England, or New Zealand -- and how many different accents and pronunciations we hear. I think it's pretty much the same with every other major language whose speakers are spread out in a wide area.

Oftentimes, what determines the pronunciation of one word is the word that immediately follows it. In the examples you cite (y usted), the Y gets buried because it's cumbersome (and unnecessary) to make two separate sounds out of those words, so the Y tends to slide right into the next word, resulting in something that sounds like "yoosted" or just plain "usted." You'll notice that this is usually the case when Y is followed by a word that begins with a vowel. In the second example, Sandra begins with a consonant, so there is no sliding from Y to the S. It requires two separate sounds. We do similar things in English. For example, the phrase The End is actually pronounced Thee End because End begins with a vowel. If you were to say The End (pronounced Thuh End), it would feel clunky. But if the following word begins with a consonant, the Thuh form of the pronunciation would apply. Example: The Boy. We wouldn't say Thee Boy. All of this goes to say that every language does this. Certain sounds are modified to make them easier to pronounce.