Everything should be covered up to 36,000 miles or 3 years, after that stuff drops off til 5 years 60,000 miles, then it's just Power Train for 10 year, 100,000 miles (original owner only)... unless you have extended warranty of some kind.
As for wear, it depends on if the wear is due to defect or not. If you can prove the leather has a defect or worn abnormally then you might have coverage. Of course there may be statements in the manual regarding leather care that you would have to make a statement about following. So check your manual.
This can be tricky to have them replaced and it can depend on how good the dealer is. We had a 2003 Sorento and within two years the out board cushions on the front seats were showing a wear line going through the gray colored material. By the way they were leather seats. the dealer replaced the covers on the front seats with no haggling. Turns out that to Kia the seats were leather on the insert area and not the out board cushion area. This made us happy and we had that vehicle for 10 years and after being replaced they never wore thru again. Now on the 2012 Optima that we bought 7 months ago at the same dealer (we have it with biege leather) the leather is much more supple and softer than our Sorento was. The service guys did mention that the leather is again only on the insert material and the outboard material is a better quality vynal material. Believe me I use a lexol leather and viynal; cleaner and conditioner on these puppies. Goog luck in getting the dealer to replace your seat material.