I read it today for the first time, and I was very pleased and surprised to see that it somewhat resembles the method used by Powers & Perils system, albeit the latter is even more logical, in my opinion (but more on this, later).
Instead of assigning hit points based on which character class you belong to (as is used in AD&D where a fighter gets a 1d10 or 1d8 if I recall correctly), the system in TG make the following reasoning: add your scores of both strength and stamina (here, Stamina is different from the concept of Constitution; in a nutshell, the former represents your ability to withstand fatigue and exertion, the latter is your physical health).
Once you come up with the sum of these two attributes, depending on how high that number is, you are entitled to roll a specific die for determing your actual hit points (which, in TG are called “Hits to kill” or HTK).
So it’s as if (under AD&D system) you were not automatically entitled to roll a higher die for your hit points just because you are a fighter whereas a mage may roll no more than 1d4; in fact. AD&D seemingly depicts any magician as a fragile and weak creature who spent all his days doing nothing but studying over dusty tomes of magic- in Thieves guild if a mage has a high rate in stamina or strength he can have many more hit points than we are used to expect.
Powers & Perils goes even further than this and in my opinion is one step beyond: though the system is quite similar to that found in TW that I just explained, in P&P- depending on your scores in stamina, constitution and strength you are automatically assigned a certain number of hit points- without even having to choose a specific type of die by which rolling your hit points (hits to kill).