That may be correct, but I chose the word "platform" very carefully. Most ARM platforms to date, whether dev kits or final product have been aimed at smartphone

That may be correct, but I chose the word "platform" very carefully. Most ARM platforms to date, whether dev kits or final product have been aimed at smartphones, tablets, consumer devices (wireless routes, NAS etc) or fully embedded systems (SD cards?, hard disk controllers, etc). Apparently in those applications, nobody cares enough about ECC to bother. Well, that and the fact that the memory is soldered on in most cases and the total device cost extremely low (compared to servers). So you are expected to simply replace your system entirely in the event that there are memory errors you notice. And hopefully nothing goes wrong that you don't notice. Also, I suppose technically if you were only worried about bit flips due to solar activity, then a tiny amount of RAM on a tiny chip has less surface area and fewer bits TO flip than your standard full sized DIMM.