Earlier quoted context omitted.
Why is that more useful than a removable SD card?
I think the comment was a bit tongue-in-cheek. The underlying storage tech between is the same, but eMMCs have a controller that handles the actual layout of the data. In a removable SD card setup, this is handled by the CPU, which of course has many other things to worry about. Having its own controller makes eMMCs more reliable.
Maybe there is some part that eMMCs have that SD cards don't, but SD cards absolutely do have a controller that does layout (wear levelling). It doesn't do the filesystem layer, but IIRC eMMC's don't either.
AFAIK the only reason SDs are less reliable, is because they're cheap and the socket can be loose, causing corruption during a write (or wear level). It would be interesting if you know of something logically different that also makes them less reliable.