Airport Extreme not compatible with some ISPs?

[MacSyn]

I am thinking to get one of this Airport Extreme Base station. So according to Apple's website, it says: "Some ISPs are not currently compatible with AirPort Extreme." Why? This really confused me. How do I check if my ISP is compatible with this airport extreme?

 

[Eidorian]

It means the PPoE support. If your router provides you with an IP regardless of the device plugged in then it's not an issue. You might be locked in by MAC address though to one device.