I have a feeling the replacement units are of higher quality. We haven't seen any posts about a replacement headlight unit having any problems yet. Famous last words though....3 days after passenger-side LED accent strip DRL failed on our 01/15 built 2016 CX-5, we found the driver-side LED DRL also failed. I'm amazed the precision quality on lifespan of the LED DRLs as both failed within 3 days! Strange thing is they're both not dim or flickering, but the whole accent strips are off.
I guess we have to consider ourself lucky having both LED headlights failed within the warranty period and not to worry about if the second one would fail after the warranty period. (whistle)