There is an MTR package for OS X: http://rudix.org/packages/mtr.html

It's all PPPoE in Cambodia, most rate limiting is handled via RADIUS I'm guessing. It depends on the ISP. Some ISPs have a whitelist in hand with their deep packet inspection, for example traffic identified as BitTorrent or VPN gets 100% throughoutput. Again, competence difficulties. There are many many many common misconfigurations in local ISPs that are very very easy to, ahem, take advantage of, for getting the actual maximum of the port in the switch you're connected to.

In developed countries you usually just get the speed of the port you're hooked up to, so the core routers and switches take care of the limiting. Here our speeds are much slower than port throughoutput and probably need to be handled by software.

It's also common that ISPs just straight up lie. They'll tell you that your maximum is 10 Mbps because the switch in your neighbourhood is 10 Mbps. And then they don't tell you that you're sharing 10 Mbps, and that the only reason why you're getting faster conns at night is because your neighbours are asleep. And speeds will vary depending on the amounts of customers in the same area (hooked to the same switch).