Rockets have been 'reused' for quite some time now - you may remember the Space Shuttle ...
The boosters were recovered and recycled. And the Shuttle engines could be reused after considerable refurbishment and testing (several months worth).
Yes, yes, I realize we're much smarter now, and Space X first stages will - against all previous experience - be reusable for an unstated number of launches. There is plenty of annoying cost information around that shows that reusing the first stage doesn't make a colossal amount of difference to the overall launch cost. The second stage would be far more reusable, if you could figure out a way to get it back (see Space Shuttle). The key is launch frequency, which is why Mr Musk is floating the idea of thousands of satellites - to make his sums work.
The reality is that SpaceX has a strategy of temporarily undercutting everyone else to win business, but with higher costs than say, the Russians. Their long term strategy needs a huge number of launches to turn reuse into an advantage.
Nonetheless, SpaceX is in a far better position than Tesla, which is what I started this discussion about. For NASA work (including R&D), they actually get significant payments up front, topped up with progress payments. Nice work if you can get it.