The question has been on everybody's lips since the rumours of a full Gran Turismo sequel on PS3 first emerged: why not PS4? Yesterday, it was confirmed that Gran Turismo 6 will launch on PS3 before Christmas this year, directly alongside - not to say competing with - the launch of Sony's new home console.

Speaking after the game's announcement at Silverstone yesterday, Polyphony Digital CEO and Gran Turismo mastermind Kazunori Yamauchi left the door firmly open to a PS4 version of GT6 - eventually.

"We actually do have a PlayStation 4 version in mind," Yamauchi told a table of journalists as road and race cars thundered around the storied Northamptonshire race track outside. "So for this holiday season, we thought that it would be best for users to release the PlayStation 3 version. I thought the best scenario would be to have the game come out, to have new content and new DLCs every month, and updates coming in for the game; and once players have thoroughly played out the system and played out the game, if the PlayStation 4 version just came out naturally in the progress, I think that's the best scenario."

Asked if it would be possible to transfer your progress from one version of the game to the next, he could only say: "Probably."

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Whilst the timing of GT6's release on PS3 seems counter-intuitive, Jim Ryan, president and CEO of Sony Computer Entertainment Europe, pointed out that Polyphony has a tradition of developing the technology of its race simulator over two versions for each PlayStation platform.

"If you look at the difference between GT and GT2, and GT3 and GT4, the change is not incremental. It's absolutely massive," argued the plain-speaking Sony boss - not without reason. "We're very confident that you'll see the step change between GT5 and GT6 as on the previous platform iterations. So there's that: a sense of very much unfinished business on PS3."

Perhaps more significant, though, are the financial considerations. Gran Turismo is one of Sony's titans, a commercial juggernaut that has amassed over 70 million sales in the course of its 15 years - fully half of those in Europe. Gran Turismo 5 has sold an impressive 10 million copies on PS3, and plans for its sequel include a much more extensive programme of paid post-release content. In other words, it's a cash cow. Although Ryan had to dance around the point a bit, he implied that such potential would be wasted on a new platform.

"The 70 million global install base of PS3 to market to... that is obviously very compelling," he said. "It's not proper for me to talk about our internal economics too much, but an intelligent man will look at an install base of 70 million, and look at another platform with an install base of zero, and you can quickly work out where the economic potential lies."

Once again, he brought PlayStation tradition into it - and once again made a fair point. "PlayStation, I think, has demonstrated a very strong track record in prolonging the life of its platforms. If you look at the amount of business that we did on PS1 after PS2 was introduced, it was a lot. If you look at the amount of business that we did on PS2 after PS3 was launched, it was a lot. We absolutely intend the same thing to be the case with PS3 once PS4 comes along."

The timing still feels awkward, though. Is this scheduling clash really what Sony planned all along? Sadly, at yesterday's brief and crowded interviews, I didn't get a chance to ask either Ryan or Yamauchi that question. My guess would be that GT6's release ended up being pushed back a year or so by the long delays in the development of GT5 - yet it was still started too early, and relied too heavily on GT5's tech, to be moved easily to PS4 without further delays and some cost to its potential sales.

After those initial rumours, many baffled commentators speculated that Gran Turismo 6 would end up overshadowed by PlayStation 4. But after yesterday's confident and glitzy showing from what is now an icon of the automotive industry as well as a gaming megabrand, I can't help wondering if it will be the other way around.