My take is that video game console manufacturers have always been closed systems and there is a tendency for the manufacturer to protect its edge as aggressively as possible.
Both Sony and Nintendo have taken aggressive policies to protect their market lead against would be up-and-comers. In the case of the Xbox 360 it is an older system and clearly there are concerns about content looking better on the PS3. But at the end of the day the market will decide. If good content starts showing up on the PS3 but not on the Xbox 360, consumers are likely to balk. So it is really a balancing act for Microsoft.
These types of policies are very much the norm with content distributors (and physical retailers). Microsoft is the current leader in HD game distribution, so it is only natural that we would see the market leader implement policies that continue to give themselves a competitive advantage.
That being said, these policies are not absolute as we have seen many games release with ‘exclusive’ content available on non-Microsoft platforms. I am sure Microsoft takes things on a case-by-case basis to maximize the value they provide to their consumers. I definitely believe Sony is in the right to at least express these concerns to the industry, but I do not blame Microsoft for having these policies, which are optionally enforceable, in place. And while Sony may chagrin, I do believe that conflicts like these ultimately result in new business strategies that enrich the consumer experience.