How reliable is the AC power? I had an original Compaq Deskpro computer years ago that would happily survive a power hiccup that killed everything else in the office.
Perhaps you're having power problems that the Netfinity can handle, but that the SME cannot, or perhaps the Netfinity is set to restart after a power outage, but the SME box is not.
Or, I've seen Windows servers that shut themselves down because of UPS software ("What!? I can't talk to the UPS? I'll shutdown immediately!")
Or, I've seen lots of systems with poor CPU cooling that reboot spontaneously.