We have to speculate that due to EA's licensing of the English Premier League either Arsenal or Chelsea must be dropped to accomodate United and the legal text on some box art points to it being Chelsea that lose out.
Also mentioned in the press release is the upgrading of the online mode in the PS2 and PC versions to accomodate eight players via four systems. Due to the lack of a mention this also sounds like something the 360 version will miss out on.
SORRY KE ESTE EN INGLES PERO LO SAKE DE OTRA PAGINA