Usually, xbox marketplace downloads are the same price as NEW discs (not used). As the prices of the new discs come down, so do the prices on XBL. Pick any game title and check it on Game Stop .com and it will probably be the same price on XBL. However, the used disc prices are usually WAY lower that the downloads.
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I'll go digital simply because I currently have every game I've ever bought, so trade-ins are not a concern for me.And, I find now that I'll play 10 arcade games before switching discs, just becasue I don't feel like getting up to change the out the disc. But they really need to make an offiical announcement regarding the bonus content. Just tell us we'll get it automatically as long as we download the game the first week and everyone will be happy.