18650 refers to the cell form factor--the size and shape--and has nothing to do with the chemistry inside. It's like saying two PC motherboards are the same because they're both ATX.
The cells in the original roadster were 3.7 V / 2100 mAh vs. 3.6 V / 3100 mAh for the latest. They're both 18650 cells--completely different chemistry.
More specifically, Tesla's shipping Panasonic NCR16850A cells with Panasonic's newish LiNiCoO2 chemistry - same as in a lot of more modern laptop batteries. The Roadster was presumably one of their older cells like the CGR18650.
The cells in the original roadster were 3.7 V / 2100 mAh vs. 3.6 V / 3100 mAh for the latest. They're both 18650 cells--completely different chemistry.