That's a very solid argument, and it's very similar to those I have heard before, and I still acknowledge that the arguments themselves are very sensible; however, I still just can't buy it, I'm sorry. It's similar to those who, in the face of personal experience and very reasonable explanations, just cannot accept the idea of the existence of God; no matter what you say, it just doesn't register with them (not trying to change the topic here, just making a comparison). I'm just not seeing it, and I have some development and support experience myself, so I'm not shooting totally in the dark here. Still, I admit I really don't know fully how it breaks down, but I'm not buying the thin margins argument at all.
Where I got that price from was a software download site I visit often, and the person who had listed those prices did say that they had not been confirmed (or even commented on) by Microsoft, so they are entirely rumor. What I heard was:
Home Basic - $256 USD
Home Premium - $511 USD
Vista Ultimate - $639 USD
Vista Business - $840 USD
Vista Enterprise - $1033 USD
Those prices are entirely out of line, in my opinion. Now, I'm not sure if the figures you used are estimates, and if they are, how accurate and realistic they are, but I'm not going to believe that it costs 4 times as much to make, market, distribute and support the Enterprise product as it does to make the Home Basic version! If those numbers are anywhere close to accurate, then they'd be losing money on the upgrade versions (surely it doesn't cost any LESS to make the upgrade version), and the vast majority of sales are very likely to be upgrades, right? Adobe, for example, sells Photoshop for $650, unless you're upgrading, in which case you get the exact same product for $170. Come on, how much does it cost to produce if they can stay in business (and thrive mightily, I might add) selling the majority of copies of that product for $170 dollars if it REALLY costs 90% of that $650 to produce it? The same math would have to apply to Microsoft; if it costs $450 to produce the Home Premium version, for example, they'd lose money selling the upgrade for $300 (which would probably be in the neighborhood of what the upgrade would cost).
Beyond speculation, I would think it should be relatively easy to check if Microsoft's profit margin, overall and per-product, is really 10%, which might be true, but I doubt it. Pennies a day you say? $500 over five years would be about three pennies a day. How about a several hundred million people paying three pennies a day into your coffers...that's a very, very tidy sum!