Ok... I don't know what the hell that was meant to mean, so I'm going to try to address the points raised in reverse chronological order. Let's get started.
Weather's not in GT4 by all accounts, so there'll be no Americans racing on dry tarmac, Australians stuck on wet or something equally ridiculous.
Now, real weather CAN physically affect internet connections on occasion. It can drop connections entirely, cause damaging power spikes, or it can just lead to more line noise and thus, more packet loss. Packet loss is when packets are lost in transmission, they aren't received at their destination. This happens a lot with dial up internet because it basically uses voice to communicate. Dial up works over ordinary phone lines by sending sound signals. If those signals get messed up, you lose part of your message, just like when you're talking on the phone and some crackling or whatever distorts the person you're listening too.
The lag issue: lag collisions happen a lot in NFSU as S13KS mentioned. However, the large reason for this in NFSU is that you have people from different countries racing each other. An Australian and an American racing each other will have a large delay. I've found when you race people from the same location as you, the racing is fine, so whilst it IS a network code issue with NFSU, EA aren't SOLELY to blame.
I'll try to explain the lag problem with an example.
We have two racers, they're right behind each other. The one in front (Car 1) starts to turn into a corner and brake. The second car (Car 2) does likewise. The first car for some reason suffers lag, so the message that Car 1 is turning and braking gets delayed by half a second. Not a lot, but in close quarters racing, it can be big. So, Car 2 doesn't know what Car 1 is doing he hasn't received a message saying he's braking, turning, accelerating or anything, so the game assumes he's doing nothing, so the car would basically come to a stop like you'd just let go of the controller. Car 2 collides with Car 1, because Car 1 has basically stopped on the racing line. Car 2 had no idea this was going to happen. So Car 2 loses all of his speed and momentum from the crash. However, Car 1 ACTUALLY took the corner normally. Car 2 just never got told. So Car 1 happily races off, not knowing anything ever happened, because as far as he saw, nothing ever did - he just drove around the corner normally. Car 2 however suddenly finds out that Car 1 was never there, and that he is in fact racing off into the distance. This doesn't change Car 2's situation, he's still lost all his speed and momentum and time.
That rather longwinded, obtuse explanation hopefully gives a bit of a picture of how lag is a problem in online racing. It means cars randomly stop in front of you and you crash, but really, the car you crashed into was never there. So you suffer and the other driver never notices a thing.
You have to appreciate that the bits of information you're sending are travelling from your house, to a local exchange, to your Internet Service Provider, to their backbone connection, to another backbone, to an undersea fibre optic line, to another backbone station, to an Internet Service Provider, to a local exchange, to your opponent's house. In the case of America Australia that's about a 12,000km journey if not more, and it makes that trip within 0.2 seconds.
Sven's idea of smart ghosting is a beautiful one, something I raised a while back when we were discussing the penalty system. There needs to be certain rules, like different speeds and proximities between the cars before the ghosting will come into effect. Remember, we do want race rubbing and we do want slipstreaming. It's a complex one.
S13KS: If you listen to Sony every PS2 should only be connected via broadband, however there's no way to force people to have broadband before you let them connect that I know of.
Now, what I'm not sure of in that respect is this:
I installed my network adaptor and configured it for my broadband connection at home. However, it worked at my friend's house and he only has dial up. Now, what I'm not sure is if during the initial configuratino it employed some sort of check with your ISP to confirm you have broadband, and once that's certified, it forgoes it each time you connect. So, if I had just installed it freshly at my friend's house on dial up, it may have been rejected. The solution to that is to simply download an pre-configured network settings file, which you can get off the PS2 memory card via an Xport. Then you'd just have to change a few things like ISP login and you'd be set.
