Why would familiarty with nV hardware versus Xenos result in higher quality textures and better player detail? Both are just ordinary functions of the hardware in poly models and texture resolutions. They both do these functions the same way, no? Porting shaders might not be straightforward, but that shouldn't affect texture or model detail.
Simple Answer: Look at the PC. ATI and NV GPUs, with very similar architectures, trade blows back and forth in games
designed to the DX API. Sometimes we will see 20-40% difference in performance in a game, and then flip flop in another game. A lot of that has to do with how the game was designed and what features are leveraged as core technologies and their implimentation and optimization.
It is not hard to venture why a game being designed
around a GPU like NV40 would port well to a G70 derived GPU. G70 is just a bigger, faster NV40.
Now take a game that has (a) an engine built around NV40 and (b) art assets built around NV40 and then asked a lower level dev team to match the port quality of a classy act like AM2. Heck, I am willing to bet AM2 can make a game from scratch significantly superior to these other guys, let alone port a game on an easier dev path. Toss in the fact the fact we know there are some quarks to Xenos, specifically in the API and drivers, and a less-skilled dev team doing more work is going to get less results.
Think of it this way: Sega gave their AAA team the easy job and gave their B team the hard job. They both get 18 months to port. The better developer with the easier job is going to get better results.
There is a message here, but it isn't about hardware.
The message is this: Sega is putting money on the PS3. Hardware is a mere abstraction to the end result. If companies like Sega are going to (a) build their games around hardware that ports well to the PS3 and (b) stick their best developers on PS3 versions of games, we can all deduce that Sega is behind the PS3 strongly and that the PS3 will get the better looking games from Sega in many situations.
Hardware is relevant, but it really comes down to developers. You stick Kojima on the Xbox 360 and you
know he is going to make one of the top 10 looking games on the platform; and vice versa you stick Bungie on the PS3 and you know they are going to turn out a nice looking game. Part of this is these devs get time and money to reach their visions, but the other part is straight up skill. Comparing a B level dev team porting their game is a case by case thing. Until we know more about VT3 there isn't much to say. One thing I have noticed is the PS3 version has really nice self shadowing which seems to be lacking from the Xbox 360 version.
Are the different developers using different art assets? That'd be pretty crazy and wasteful, but to me seems the most obvious reason for the differences rather than variations in hardware. I expect the differences between Xenos and RSX to matter in XB360>>PS3 ports where the features of Xenos are used effectively and RSX hasn't got those features, but going the other way round what has RSX got that Xenos hasn't that makes porting assets hard so that they'd be downgraded?
The time, budget, and skill of the dev team also come into question mind you. Take a look at Venom (Prey) and Raven (Quake 4) and how limited tools and time significantly hampered ports. Financially it was not viable to do a clean build and reading the Venom blog it was made pretty clear that they were waiting for the code from Raven, and then when they saw how choppy Q4 was and how hacked the code was they had to start fresh, etc with limited time.
At some point we will begin seeing games developed independantly by quality dev teams. e.g. Madden has 2 dev teams. I don't know if one is better than the other (so there is that factor), but Madden is a case of a company having 2 teams build separate builds designed for the platforms. I think future games like that may tell us a little more about the hardware, but more likely looking at the average budget of games, developer skill and profiles, and the average quality of games across the board will tell us more than individual titles. i.e. Trends versus anectodes.