One problem with the electronic odo's and other displays is that they are lit every minute the car is running, so the bulbs have a short life compared to the instrument lamps on older cars.
That said, your early bulb failure is a tad unusual. Most cars seem to make 4-5 years before one crops up. I had to replce the bulbs on both our 1998MY cars this last summer.
These bulbs are usually classified as wear and tear, just like any other bulb, and are not covered by your warranty. However, I would ask the dealer to cover it, and they might.
1998 C230 "Black Betty"