One data point does not a trend make. Let's put this in some context.

While the PS4 is clearly no PS2 in the U.S., its sales aren't anything to scoff at. Yes, January wasn't all that great, but what does this chart show? The PS2 and PS4 both suffered at 82% drop from their second December to their second January. Their January sales were also about the same as their Q2-Q3 baselines (Sept. of last year had Destiny, which was a huge system-seller). Meanwhile, the PS3 had received not one but two rounds of price cuts in 2007, first with the 60GB model being cut from $600 to $500 in July and a new 40GB model released in November for $400, the first PS3 SKU to retail for that price. Granted, the PS4 is also selling at $400, but sales are rarely proportional to price, even among systems of the same brand. All things being equal, the least expensive system in a generation should be the best selling, and price cuts are one of the most consistent and persistent boosters of sales, but we shouldn't expect any specific range of numbers from a system selling at a specific price point. The fact that the PS3, after retailing for an insanely high price point by any standard, was now available for what the 360 was at launch probably reinvigorated interest in the system.