The thing that's fascinating about people with that much money is that they have a lot of freedom to express themselves within their lifestyle.
Cars are a very particular expression of that. So Larry Ellison has a custom all-aluminum roadster, Steve had his German sedans, and ESRI's Jack Dangermond is noted for driving a Taurus wagon.
But just having a Mercedes AMG isn't the same as leasing a new one every six months. But as has mentioned, he may have simply leased the same vehicle on successive six-month terms. That's a very good point and I'd suspect that was in fact the case. It's an even cleverer maneuver and simply sounds more like what Steve would do.
I suppose it makes up for him not living in a gated fortress.