All of the costs cited are rounding errors in comparison to the scarcity of good developers' time, especially developers capable of delivering product across iPhone / Android / web.
Developing on "an old clunky win laptop" in particular is far from zero cost.
I always love how much developers think they can save skimping on hardware. $700 is a day worth of downtime. My Macbook Air is easily worth $4000 to me now because it broke 3 times and they turned it around each time in under 24 hours. When my windows laptop breaks im with out it for 2 weeks requiring me to purchase another one.
Who said anything about skimping on hardware ? My point was that you don't get the same horse power for price ratio on an apple laptop that you get from a Windows laptop. As for support it depends on your geographical location. You were able to get your mac air replaced thrice within 24 hours each time and I get similar support for my Windows laptops. It took me 4 days just to get a human being to respond to a problem I had with apple up-to-date support.
Developer time is more valuable than hardware costs hands down. The horse power that you can back in return for that hardware cost varies between apple and windows.
Developing on "an old clunky win laptop" in particular is far from zero cost.