US survival rates from major diseases are much higher than in other countries and detection is better. The value of this is equal to full percentage points of GDP (he estimates 4%, using back of the envelope numbers, but the exact number isn't important, it's the order of magnitude).
This also neglects the notion that having a non-socialized health system means that drugs get developed. If we socialize, it's gonna be a LOT worse for everyone because we will have created a monopsony that disincentivizes medical R+D. The improvement of the US in prostate survival from 7% worse to 20% better (for a swing of 27%) would be even more if the US didn't export its medical technology. In a sense, Europe and Japan "free-ride" on our medical system, and thus this 27% is an underestimate.