Scott, it seems to me that Netflix hasn't really thought this out. Let's face it...right now, the content available via streaming is not great. I would estimate that at least 90% of the available movies are, at best, B-movie crap that would make Ed Wood blush. There are very few first-run movies that I want to see. As a result, my very occasional use of streaming does not impact my internet bandwidth usage. However, if Netflix does provide more first-run streaming content, then my bandwidth usage will may hit some threshold set by my service provider. My ISP price may go up or my ISP download speed may drop as a consequence. Either way, I am not a happy camper. People may like the convenience of streaming, but I have a feeling they won't like it THAT much when this reality comes to fruition.
Yes, maintaining an inventory of DVDs and Blu rays is expensive, but it is a cost of doing business. I, for one, would be willing to pay a (slightly) higher price for the DVDs/blu rays and, with it, the choice from a much larger catalog, the better picture quality, and not having to worry about my data usage.