Earlier quoted context omitted.
"After 5 years/70k miles, the battery will probably still be at 95% capacity" No way. I'd say you have 75% tops (probably less with 70k miles). And unless you pre-buy a new battery you're going to be looking at a $20-30k replacement cost. Also note that it will likely be out of warranty at that point. And that Tesla values them at roughly $1 per mile (the price they give you for purchasing a loaner).
The battery replacement cost is $12k for an 85kWh: http://www.teslamotors.com/blog/2013-model-s-price-increase And the retention is closer to 85% at 100k miles: http://www.plugincars.com/tesla-roadster-battery-life-study-... (Keep in mind, the Roadster has a previous generation of battery pack technology)
And Tesla itself would disagree as it has stated 70% after 7 years/100k miles.
I'd be careful to compare with the Roadster either way.