OK I just noticed this today too, had noticed when the iPad came out and thought it was due to server load!
So, my home connection is Clear WiMax and the URL failing is indeed:
http://C2C738.r.axf8.nethttp://images.apple.com/mr/a.gif?a=C2C738&v=0 this URL doesn't appear in View Source for the front page, but could be called in associated javascript or CSS files.
The previous solution to setting the DNS server to what your router is using only speeds things up, it still is getting looked for, it just fails faster!
The real question is are the DNS servers between you and Apple compromised in some way?
Testing from work, on an AT&T Worldnet connection, there is no such URL that is looked for. Seems like some routers got hacked... 😟 poo.