[pclmulqdq]

On-die ECC is so they can give you a memory array with a few faults. It's a yield enhancement not an introduction of ECC as you think of it.

Adding protocol-level ECC on top only helps, although it is somewhat inefficient.

[thfuran]

Similar to SSDs, which are constantly switching to less and less reliable cells for density and now need fault correction built in to function at all.