Why did they change this? Over the last few days, I am still be prompted for my userid and password.
THEY did not change anything. You have been getting lucky. Contantly restarting ATV and your router can, and usaully will change your IP. When that happens you will have to re-authenticate.
The other response is correct. This is a problme by design. Networks are not supposed to be powered down every time you stop using them.