It's worse on iOS, actually... once you do get it to connect, if you put the phone back in your pocket for 5-10 minutes it disconnects from the WiFi. When you start using it again, it'll re-connect, but depending on how the captive portal is set up it may make you re-authorize. Android devices (and 'real' computers whether Mac, Windows or Chrome OS) will just stay connected to the WiFi until it goes out of range or you disconnect.

Yes, this issue is really the network operator's fault for stupid configuration, but iOS stands alone in being unable to handle it.