It's probably a mix of things like an oiling problem or something that causes the lifters to not move up and down in their bores as easily as they should and weak bearings in them that can't take the added force when that happens. There's very little friction between roller lifters and cam and it seems that this has only become more of a problem with newer engines. Don't forget GM v8s also have the same sort of problems and also started around the same time.
Even with older roller cam engines you can open one up that had engine failure from oil starvation and the cam and lifters look perfectly fine.
There are also posts kicking around other forums, usually by the same small number of people it seems, that blame the failures on lack of friction because of certain oils which cause the roller to not roll on the cam.
Seems to me if the lifters not rolling due to no friction between roller and cam I would not expect to see bad bearings in a lifter but still have the cam be perfectly fine. I have seen plenty of lifters that have a bad bearing, usually several in a set when one has totally gone bad (you can clearly hear it when rolling it on clean glass) but the cam is still perfectly fine on those lobes. Maybe the needle bearing is not rolling because of the lack of friction and going bad inside the wheel, then it eventually stops rolling and THEN the lifter eats the cam. Even if this is the case it looks to me that the larger needles solved this.
