ITunes search API returns different app icons for 60×60 and 1024×1024

You can remove the country code from the URL, so it reads http://itunes.apple.com/artist/nash-the-slash/id160526527. That gives you a valid iTunes URL, that if opened in a browser (that doesn't auto-open iTunes), appears to be the same as if the link were a US link.

However when any iTunes link is opened in iTunes itself, it will attempt to redirect to the version in the user's local store. I.e. when I click on the link you posted, I get sent to the same item in the Canadian store.

If the item isn't available in the Canadian store, I get a message like this:

So, you should be safe using country-specific store links, and iTunes will handle the redirection as appropriate.

In any of the common scenarios in which you store your Store credentials on devices under the control of others, it makes good security sense to have those be different from the ones you use for iCloud.

For example, it is common to share music among family members by using an Apple ID for purchases on all of the family's machines. If that Apple ID were the same as the one you used for iCloud, then (unless you can be sure that all family members have secured their machines) anyone who got his hands on one of those machines could potentially gain access to your e-mail, calendar, and documents (and, in typical configurations, could even log on to your machine if he had access to it).