For a 3 year old saw, I don't think it can be concluded that the casting was defective (although it cannot be dismissed either). As was discussed in the recent kickback thread, if the user plunges the saw down with the front of the saw over the workpiece, it will slam the saw to full-depth very fast and with a lot of force.
I am sure that anyone that has owned one of these saws for very long has made that same mistake at least once. Even if the tab didn't break off at the time, it could very well have fractured it.
Yes, I would still check with the service department, but I would not expect this to be a trivial repair when out of warranty. Replacing the gear housing would require the motor's rotor to be pressed out/in the gear housing, and would also require the plunge pivot to be pressed out/in from the blade housing. That's pretty major surgery.