A few facts:
PS2 can do 5.1 sound in game.
It's called DTS which is technically superior to the Xbox's DD5.1. First of all, DTS uses a higher bitrate for encoding the audio so it should technically sound better. Also, very few Xbox games, if any, actually do proper center sound chanel seperation.
PS2 also uses a different form of Pro Logic II. It can actually encode 5.1 sound. And lastly, Pro Logic II can be expanded upon in software. FFX-2 is the first console game to use Pro Logic II EX. Then, we also have Sony's sound engine which can also give higher fedelity than the Xbox's DD5.1.
Here's something else to look at.
Here is what gets advertised for the Xbox specifications:
250 MHz GPU
300 MHz Ram
733 MHz Pentium III
Here are the actual specs:
233MHz GPU
200MHz DDR Ram
733MHz Pentium III / Celeron Hybrid. (Weaker than a Pentium III)
And one other interesting fact about the Xbox:
This is a simple HDTV guide for a reference to the following paragraph:
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480i = 640x480 pixels @ 30htz
480p = 640x480 pixels @ 60htz in a widescreen format
720p = 1280x720 pixels @ 60htz in a widescreen format
1080i = 1920x1080 pixels @ 30htz in a widescreen format
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The Xbox can not do any resolution above 1024x768 pixels. What does this mean you ask? It means that no Xbox game runs at 720p. Before the fanboyism sets in and you start sending hate mail let me clarify some things. The Xbox uses a Conexant Decoder Chip for its output display. To be precise, the part numbers for this chip are [CX25871-13 / E145981 / 0134]. The decoder chip cannot accept a signal greater than 1024x768 pixels from the Xbox. While that is a lot of pixels it isnt 720p or 1080i. To get that resolution the decoder chip basically up-converts the output to fit in the 720p or 1080i format. The game is still being output from the Xbox at a lower resolution. The resolution could be 640X480 or 1024x768 or something in between but it is not 1280x720 or 720p. This means you arent getting any better quality and the Xbox isnt rendering your game at a higher resolution.
Let me add something else while I'm at it:
The PS2 is based off of a processor design that began with Hewlet Packard. It's coined as an EPIC processor. This is similar to the newer Intel Itanium chip. But the PS2 has those highly efficeint Vector Units added on. It's basically a version of a RISC III processor but with a RISC IV instruction set plus vector units. So in the end, the EE can process more instructions per clock than a standard RISC IV.
And to go even further with this.... A RISC based design uses less memory bandwidth than a CISC based design. It's all in the name RISC which stands for Reduced Instruction Set Computing. It's strength is in calculating very small basic instruction set code over and over and over and very high speeds. These types of processors don't need half the amount of bandwidth CISC based chips consume.
A standard Vector Unit in the EE can hold a small amount of micro or macro code in it's registers and process the data over and over without pulling it through the entire system bus. In other words the PS2 is much more efficient with it's code than the Xbox.
And to elaborate more on the memory issue...
The PS2 has a total of over 40 MB of ram, not 32. That 32 MB of ram isn't unified like the Xbox ram. On the PS2 you can use the full 32 MBs for graphics and code. On the Xbox you ahve to split that 64MB up. Part of it is for storing textures, talking with the main CPU, storing sound data, etc... This lowers the available bandwidth for the GPU and levels out the playing field between the two consoles.
The reason you haven't seen much done on the PS2, up until now, isn't because it is the weaker system. It's simply because developers need to use the PS2 in the way it was designed. Textures need to be streamed from the disc instead of stored on the console. When you start storing texture data in that 32MB of ram you start limiting the bandwidth to the Graphic Synthesizer making it do extra work.
I'll stop boring you now...
I will say this. GT4 Prologue is not the finished product. It is a demo, even Kikizo.com stated GT4 looks much better in it's demo state than PGR2 did. I can guarantee there will be more polish and some tweaks to the graphic engine in the months to come before the release date. I expect less pop-up, more polish, and possibly a few more effects added in. We haven't even seen water effects yet.
Xbox may have the edge in power but the PS2 has the edge in flexibility.