The 3.8 Million shipped of Uncharted 3 was in November, just shortly after a major pricecut to the PS3 itself.
They shipped a fuckton of stock not only for launch, but to maintain supply throughout November and December. Uncharted 4 has launched in May, nowhere near any significant system selling push from Sony. They likely shipped a similar number of copies (possibly less), but it's also likely that Uncharted 4 actually *sold* more within the 7 day span. Uncharted 3 needed a huge shipment for the holiday season.
Remember that despite launching very early in November of 2011, Uncharted 3 "only" sold 700k throughout the entire Month (via NPD). Looking at these sold numbers, it's very likely that Uncharted 4 eclipsed that in a single Week, in May.
When comparing these things you have to look at when U3 was launched, and *why* it launched with so many copies shipped day one.
