Good teachers will tell you that words do matter, as pronounced and interpreted by the singer. Opera audiences have acquired a feeling for the languages being sung, even if they don't know the meaning of every word and are thus grateful for the "supratitles" as well.

Old Vermin, perhaps your teacher told you to pronounce the vowels in a way that they do not differ from each other more than necessary. This makes for a more consistent sound, so that the melody is presented as a unit, as if from an instrument. For the same reason, teachers will tell you to blend the registers of your voice. Both ideals apply to opera, lied, and (European) folk song alike, with the exception of yodelling. The best folk singers follow them without anyone noticing.

Both Pavarotti and Domingo, by the way, interpreted the folklore of their countries in perfect taste. In other cultural contexts they were not quite as successful, artistically.