Personally, I was very upset when I heard about no online but I can't blame their business decisions. GT 4 is a major game for them this Xmas, and with everything from MS and Nintendo, they need to do all they can. Apparently the NA work for the online mode was done, but the Europe and Asian work was not... Guess rather than give the majority of their online userbase something the rest of the world would not get, would be a worse move. But anyways, GT4 is going to be phenomenal regardless of online play or not. Over 50 courses (not including mirrored), now boasting 650 cars, all the new modes of play (especially Drag Racing for the first time!), photo mode, flee market mode, banker mode, etc etc etc. It really will deliver the goods.
The only thing is that if GT4 is released next year online for the same price, I will be mad, everyone will. I doubt they will do that. I would not be surprised though, if the GT 4 online next year is the PSP game. It would be a sly marketing move, and would guarantee big PSP sales. Maybe they will release the PS2 GT 4 online the same day, and make the titles coplayable online.