No they are not, well, it depends on the game. Say a game is 13GB after production, the xbox 360's only support dual layer discs, so the developer will have to dumb down the graphics of the game in order to fit it on one disc (Dual layers support 8.5GB). On the playstation3 however, blu-rays are supported and they hold 25GB of storage, giving much more room on the disc for detailed graphics. If the game developed is 7GB post-development, then it will not matter what console you play on, the graphics will be the same. Often times though, blu-rays will have better graphics because of the space on the disc.
Hope this helps.