Nuance's Vocalizer Automotive VS Expressive? What's the difference?

Hello to all. I read an email that is posted on the Serotalk podcast website written by Mike Arrigo. For reference, it is podcast 171. Near the end of the email, he talks about Nuance using a new Vocalizer engine called "Expressive". For those who have knowledge on this topic, what is the difference between the older one "Automotive" VS there latest generation already named above. Aside from the fact that now the newer one has taken quite a hit with some voices in quality. I mean, why can this happen? I don't get it and for the voices that hasn't changed do you notice the quality being same, better or for worse in your respected language? Looking forward to feedback from others. Thank you Daniel