The thing is that the response will always be ICMP (either Time Expired, Destination Unreachable, or Echo Reply), and routers will often consider those low priority as well, even if the original packet was not ICMP, so it's pretty much all bogus. BTW, most Unix traceroutes use high-numbered UDP packets to probe. Windows's tracert uses ICMP Echo Requests. There's also an ICMP Traceroute type, but I don't think I've ever seen that implemented.