Why would Ping Plotter show 100% packet loss, after just a few pings, to the final hop of a site when using the TCP engine but show normal pings to the final hop using ICMP?

I've seen plenty of sites blocking ICMP echo request but blocking TCP....err...????? Something is screwy here. <img src="/forums/images/graemlins/laugh.gif" alt="" />

I thought maybe it was because I have an old beta version of WinPcap, plus, I wasn't using the latest Ping Plotter Pro version either. So, I fetched the latest of both and no change.

I don't get it. Am I just being dense? Is the reason obvious?