いくらやってもwelcome！みたいなページになってしまう。
なんで？と思って調べたら、以下のようなことだった。
You cannot access iCloud.com on a mobile device using Safari. There really is no need (in Apple's mind anyway) for you to need to access your account from the iPad.
If you have the iWorks apps - you have the files on the iPad. If you want to get to your calendar or notes - you have them on the iPad. For mail - you have the mail app. Photos ... Photo Stream.
What are you needing to access in iCloud.com that you cannot access on the iPad?
Logging into your account is meant to be done on a computer using a web browser. From there you can download files if you want to edit them on your computer.
I cannot bypass iCloud server welcome...: Apple Support Communities
iWorkとか、それぞれのアプリからiCloudにアクセスできるので、
わざわざSafariでアクセスする必要がない、ということですね。
ふーん。