Yes, but passive PoE is almost universally at 24v, and per the Ethernet spec (as quoted above) an Ethernet PHY should tolerate 24v fine. This is important as transients from nearby lightning or occasionally even coupling to power cables can produce this kind of voltage. Ethernet connectors are magnetically coupled for protection from these transients.
The problem with PPoE in these cases is, I think, not the voltage so much as the current. The continuous 24v supply may overheat the magnetic coupling transformer and cause it to fail. Some Ethernet interfaces, usually on telecom equipment and quality switches, have over current protection to prevent this. Unfortunately consumer devices usually don't.
It's important to understand this because 802.3af etc. does provide power without being asked - as a rest for a characteristic resistance on the receiver. Otherwise it wouldn't know if a PoE-capable device was connected. Up to 20v can be applied during this process but it is time limited. In general, 802.3 PoE supplies must monitor the current usage of the powered device and cut off power if it is too high or even too low for more than a short period of time. This is in part to prevent this overheating problem on devices that might, for some coincidental reason, fall into the appropriate resistance range to activate PoE.
In other words, 24v or even hundreds of volts for a few seconds is perfectly safe. 24v for minutes is likely to cause damage to devices without better protection than the spec requires. Old Ethernet equipment used to make the non-isolated components relatively easy to replace so that repairs after a problem like this were easier but now the isolation is a tiny surface mount part and replacing it will require tools and skill.