I've never seen a pilot bearing fail.  A bushing is more likely to wear out.  The idea with the bearing is that the wear is spread across the considerably greater surface area of the rollers instead of a fixed bushing.  I look at it this way: Ford used pilot bushings for years before switching to the bearing in the '80s.  Why?  OEMs don't make changes like this unless there's a reason.  The bearings are more expensive that the bushings so it wasn't cost.  My supposition would be that it solved any warranty issues they were experiencing using bushings.