"It's fairly obvious from the screenshots shown to date that there has been some significant paring back of detail on the PS3 version of the game, so what's going on? Well, the foliage is generated from transparent alpha textures and these are more expensive for the host hardware to draw.
Cutting back on them saves on performance in terms of fill-rate and bandwidth. It's also interesting to note that the alpha-to-coverage transparency type is used on both systems, but looks considerably worse on PS3 owing to the reduced resolution.
Resolution aside, the comparative lack of foliage and brush in the PS3 version is the biggest difference. In truth, PlayStation 3 owners won't really miss it. Many of the nips and tucks only really become noticeable in the Face-Off environment, and won't really impact the gameplay experience.
This is incidental detail - albeit one of the more prominent elements - so unless you have both games operating side by side you are not really going to notice it. However, it is a clear indication that Rockstar had to pick and choose where to make compromises in order to retain performance, and even then this compromise still fails to match what is being provided by the Xbox 360 version of the game in terms of frame-rate in the more action-orientated sequences."