All of my rotors had a small lip. It is from the area the brake pads are not touching. I didn't replace them because they aren't warped. I wouldn't cut them though because that will make them warp sooner. I am not sure on your 05 but my 02 and 00 both have sensors on the front pads. The sensor is embedded into the pad itself. I would imagine yours are as well. If you call a parts supplier like blauparts.com they would be able to confirm what brakes you need. Some guys file the lip down themselves to help fit the new pads. But with a slight sanding they should fit over the lip anyway. The top of the lip was the original thickness of the rotor.

I drive city I really don't do any high speed braking.(such as 80 down the parkway and slam on the brakes every 5 minutes for the traffic jams) If you do you may wish to save the money and replace them with the pads because they will most likely warp soon on you anyway. I used to warp mine in New York on a regular basis but you need to drive like an animal when you live in the jungle

 

Talk with the guys at Force Five in Concord NH about the parts.

I only replace rotors if they are warped or badly groved. If the lip is big I remove it with my grinder. Remember - what you see for a lip is more than what was origionally there because in most cases it got thicker due to rust and grime.

 

it's easy to do yourself.... I just did the rear rotors and pads on my a6..
take the tire off... remove the two bolts holding the pads.. pry the pads out... take the two hex bolts out.. remove the bracket for the calipers... hit the back of the rotors with a hammer they come off... rear rotors were $20 each at autozone... rent their disc brake tool for free with a deposit.. you will need that to TURN the rear pistons in.. you can't just push them in like most cars...
I think the front rotors are a little more money... but the whole thing should cost under $200 and take maybe 2 hours for you to do.. Dwight