Yes, but NTP as a time service (client/server mode) is safe. A request has a single response and their lengths are symmetric (that's actually a requirement for accurate synchronization). The problem with amplification is in the optional monitoring/control modes of the protocol (modes 6 and 7 as used by the ntpq and ntpdc utilities respectively), which should be disabled on public servers. Unfortunately, there are still some old misconfigured servers causing problems for a lot of people.

In PTP the problem is in the synchronization protocol itself. A master in the unicast mode is basically a programmable packet generator. It sends sync/announce messages at a rate and duration specified by its slaves, and the address can be spoofed.