It seems that the browser bundled with the Playstation 3 doesn't support HTTP compression. This is quite strange for a modern browser release, the last browser that we are aware of that doesn't support compression is IE 5 on Mac OS X. Hopefully this situation will be resolved via a future firmware update.
On a similar subject - we are not sure if HTTP compression is supported on either the XBox 360 or the Wii, if you know please post here to share your knowledge.