Would you like to buy content on Xbox Live in specific dollar mounts, not mysterious points?
This option is available through Games On Demand but nowhere else. I've speculated it's a testing ground for a more widespread feature (alongside Zune Marketplace's text search), though Microsoft's been quiet about specifics. When asked by Game Informer about the possibility, they didn't say no.
"It’s Microsoft points right now, and those have been very successful for us. Especially at retail – people buy tons of points cards and bring them home. We continue to think about it. I’ll put it this way: we want make it as easy as possible for people to have the entertainment experiences they want," said XBL general manager Marc Whitten. "I will say that will say that we will continue to focus on making the system simple, without giving you the roadmap."
That's progress, I guess. Rest assured, I'll continue to press Microsoft on this in the future.
Source: Game Informer