Difference between Pioneer and Pioneer Premier?

[ski]

I've been reading the audio forums for my model of car, and a lot of people recommend Pioneer Premier head units. Here's the thing though, from webpage comparisons for similar models, I don't know what makes a Premier a "Premier" over a regular Pioneer model.

Example:
Pioneer Premier DEH-P590IB (http://www.onlinecarstereo.com/CarAudio/ProductDetail.aspx?ProductID=17673)
Pioneer DEH-P5900IB (http://www.circuitcity.com/ssm/Pioneer-In-Dash-Player-DEHP5900IB/sem/rpsm/oid/171800/catOid/-13089/rpem/ccd/productDetail.do)

All I can see by initial inspection is that there's a faceplate difference. /boggle

EDIT:
Where's the delete thread button when I need it! I was curious and just copied and pasted the title into google and found my answer. Premier has one extra year warranty, and that seems about it.

[hapoo]

All I can say is this... if your going to get a new deck, get one with HD Radio. Its pretty much doubled all my stations since most of them have 2 channels, and some stations like KROQ sound unbelievable!

[ski]

I've seen head units with built-in HD Radio tuners, and they advertise that there's no other equipment to buy... so is it safe to assume that it uses your regular AM/FM antenna to receive it?

[hapoo]

yup, if there is an HD feed on the station your listening to, it automatically switches over. And after listening to the crap that was Sirius radio I can tell you that most stations sound better than Satalite.