Microsoft's Xbox is the most costly platform for game development, followed by Sony's PlayStation 2 and Nintendo's GameCube, says the latest report by the Computer Entertainment Supplier's Association (CESA) in Japan. This week's issue of Famitsu covers figures from 2004 given by CESA, which calculated the average development costs for games on current-gen platforms. The reported figures are based on development fees that were voluntarily disclosed by 28 companies.

According to CESA, the Xbox is the most expensive due to the platform's high-end hardware specs. Development figures taken from 13 Xbox games came to an average of 202 million yen ($1.85 million), more than double the cost of other platforms.
The PlayStation 2 ranked as the second-most-costly platform to make games for, with development figures for 194 games averaging 96 million yen ($877,000). The GameCube came in third, with figures taken from 11 games averaging 90 million yen ($822,000).

IMHO, x360 play xbox 1 games with better quality, dont think its just emulator like in PC, its a full accelerated emulation with enhancement according to microsoft, but it only support certain game, not all the game can be backward compatible, such as DOA volleyball...