This must have got lost in the fog somewhere. Microsoft announced in Cannes last week that Silverlight ads are to be shown on Xbox Live "within the next year".
"By extending support to technologies like Silverlight, Xbox Live will offer advertisers and creative designers scale and reach with their campaign creative assets, enabling them to build and deliver interactive, interconnected experiences that are unlike anything else on television, and extend these experiences across multiple screens – the TV, the PC, and Mobile," said the firm.
That piece specifically says "Xbox Live" - stands to reason that you're not going to be seeing any ads unless you're connected to the internet - but there's no specific about where the creatives are actually going to appear.
And you're not going to be running a blocker on your 360. Best prepare for adageddon.