@Gertjan Other one are missing,

because of google being blocked in china, cellphones and multiple chinese garbage browsers (360browser, etc...) are usually using one of these URL:

https://connect.rom.miui.com/generate_204 (Xiaomi) http://www.qualcomm.cn/generate_204 (Huawei) http://www.265.com/generate_204 (Google Chrome, Asus cellphones. This website is owned by google)

I also heard that nintendo devices are using http://conntest.nintendowifi.net for captive portal detection
but anyway, i don't think that's very important..