Why did PS3 drop so much in the US market compared to the X1
The average American consumer always chooses the cheapest console that has 3rd party support. The console that launches the cheapest always gains huge traction and generally wins the gen unless it releases year(s) later than the competition. Prices are launch prices.
SNES ($199) > Sega Genesis ($189) (though SNES ended up selling a little more, the cheaper Genesis gained huge traction and market share compared to Sega Master System vs NES)
PlayStation ($299) > Sega Saturn ($399) (N64 launched 2 years after PS and lacked 3rd party support)
PlayStation 2 ($299) > Xbox ($299) (Xbox and GameCube both launced 1 year later than PS2 and lacked 3rd party support)
Xbox 360 ($299) > Wii ($249) > PlayStation 3 ($499) (360 was $50 more than the Wii but had strong 3rd party support, the 2 are practically tied in the US)
PlayStation 4 ($399) > Xbox One ($499) > Wii U ($299) (Xbox One has been doing a lot better since its price drops and Wii U isn't winning because of its lack of 3rd party support)