Dual layer dvd discs hold 7.97Gb, not 9.4gb (dats single layer on each side). According to Nero dat is 8152mb and there has to be some overlaps in the 360 version, so i think Square has to use 5 entire discs 100% to make the 360 version exactly same as PS3 version (if they want to).
The only thing interested me is dat they used a dual-layer disc (they could save some bucks using single-layer ones) and still spared 12.4GB space. They could easily fit higher bitrate FMvs and uncompressed 7.1 audio,but they didnt just to promote the 360 version. MGS4 used a dual-layer disc completely, Killzone2 was on dual-layer too.
Uncharted 2 used every single bit (not byte) left on a single layer disc. Thats why Naughty dog had to compress those bonus 'making of' videos to really low quality using variable bitrates, they dont even complain to Sony !!