Apple has been known to previously block apps because the competed with their own offerings (http://almerica.blogspot.com/2008/09/podcaster-rejeceted-because-it.html); this is likely a preemptive strike, with the Kama Sutra as a convenient excuse. I wouldn't be at all surprised if Apple is going to try to challenge Amazon in the mobile e-book market, and of course, they don't want to have to compete within their own device.

Actually, Microsoft has patented the Ribbon, so open source products can't use it.