I like your original question...how the hell did a thrust spacer get into the axle tube? That shouldn't be able to just stick to the end of the axle,should it?
Now that I see this thread lol...
I can see the advantage of roller bearings taking less power to roll and can handle the side loads in light duty applications however, they will never handle the same sideloads as a equal taper bearing. Chrysler just overbuilt their stuff for a few reasons but fact is nobody uses roller bearings up front for a reason.