I think you are leaving out several important costs from your purchase calculation.
For example, 4S has quite high Mello Roos (especially for north 4S). Unless you plan to pay that off early, you have to add that in (in addition to the HOA, which is reasonably low in 4S). Also, the various costs of home ownership.
I looked at 4S pretty extensively a couple of years ago (I work in one of the tech companies nearby and I like the area). I ended up buying elsewhere, but I might still buy in 4S in a couple of years (good schools, etc).
But I seriously doubt that I would be able to find such a deal on a purchase that it would be $1,000 less than renting.
