The cells themselves are COTS Panasonic NCR18650A without built-in protection circuits.. The management circuits are probably developed by Tesla but are external to the batteries, most likely a circuit per array of parallel cells.
Having a protection circuit per cell would be wasteful and also result in quite a bit of power loss and complexity in wiring them up.
I toured the Tesla factory in Fremont, CA last Monday. During the completely awesome 1 hour tour, our guide answered many detailed questions about their cars and manufacturing processes, including how Tesla instruments battery cells.
We were told that they instrument every single one of the 7,000+ cells for temperature and voltage.
That's an overstatement. They do not have 7000+ temperature and voltage sensors per pack.
Each of the 16 modules is split into 6 blocks where the 70+ cells within a block are all wired in parallel -- so they are going to have the same voltage. The blocks within a module are wired serially and the modules are also wired serially.
It has seven voltage measurement inputs (between each block and before/after the outer blocks) so it can tell the voltage of each block. It can also control a bleed resistor per block (for balancing). There are two temperature sensors per module.
Each module also has an 8051 (C8051F530A) that talks to the battery monitoring chip and to the data network connecting the modules to the "global" battery management system which has a Altera CPLD and (probably) an ARM CPU.
That's standard for NCR18650A cells though - they ship with no protection circuit and I believe the same chemistry that the Model S is using. The protection circuits are added by companies that buy raw cells from Panasonic.
Having a protection circuit per cell would be wasteful and also result in quite a bit of power loss and complexity in wiring them up.