I thought dead rising has no AA in gameplay but 4X AA in cutscene. Anyway is 360 the only one that is capable of change MSAA sample on the fly in game?
While not hardware specific in terms of the ability to implement, the bottlenecks or trade-offs will differ in other platforms. The main reason for this dynamic AA would be any performance hit related to tiling.
Where with Xenos, the difference in AA modes does not mean any more memory consumption as the frame/partial frame in eDRAM is converted to raw colour data in main memory, the memory bandwidth hit is a non-issue, and lastly, the ROPs are designed for full-speed sampling rate at 4xMSAA.
In the case of RSX, such a dynamic framebuffer mode will make less sense for games strapped for memory and bandwidth and/or performance due to the multiplicative nature of MSAA (increasing samples per pixel = increased framebuffer size and thus increased memory bandwidth consumption); RSX's ROPs should be able to do 2 samples per cycle following G7x, so in the case where memory bandwidth and memory consumption are not limiting factors, there would still be around 2x hit to performance when enabling 4xMSAA from doubling up on the number of cycles needed to finish sampling.
With WipeoutHD, it appears the devs budgeted for 1920x1080p, varied down to 1280x1080, which is at best a 33% reduction in pixel processing and backbuffer memory - much less variation when comparing dynamic AA.