This is not true: if a wine turns into any sort of "vinegar" then a bacteria was present that should not have been. This is considered a "fault", and won't happen normally, even after 100 years in the bottle.

Hmm. I remember tasting a nicer higher end balsamic vinegar and you're right it didn't taste tannic or acidic. But that wine did taste different, in other words it still tasted like wine more than good balsamic vinegar.