If you installed a European outlet in a US home then it would be using the same split phase configuration that a NEMA 14-30 does. But many appliances will work just fine, so long as they can handle 60 Hz and don't actually require a distinct neutral and ground for safety reasons. Likewise NEMA 10-30, the predecessor to NEMA 14-30 which is still found in older homes, does not have a ground pin.