Historically, the FD offer to the general public has a smaller booking window than the bounceback dates.
Remember, we don't have much to go on in terms of "history" for this one.
In 2006, there was no Bounceback
Free Dining.
In 2007, there were both Bounceback and Public Free Dining, and yes, the Public offer was substantially shorter than the Bounceback. However, in 2007, the Bounceback was offered to those onsite in Nov-Dec '06. That would give people only an 8-10 month turnaround to their next vacation. Perhaps Disney made it a larger window to account for the difficulty some might have had in actually thinking they could pull off a second Disney trip inside of one year. For most people at Disney, that just isn't realistic.
For 2008, we have a fairly short Bounceback - essentially the month of September only (with a couple of days in August). This was initially offered only to those onsite in September '07 - exactly one year between trips. While still hard for many, it seems to be a little more doable, especially for those who are traditionally "annual" visitors. There is also the the nice way that the offer time and travel time lined up - September for September, although Disney (for whatever reason) extended the offer to those onsite during the first two weeks of October, but did not extend the travel dates.
This is why I have been reluctant to assume that any Public
Free Dining offer will be directly correlated to the Bounceback dates. They are two different beasts, both in terms of audience and intent. One (at least partially) is to keep annual visitors returning, the other can be for anyone, but arguably is great to get first-timers there - who might then be offered the chance to become future bouncebackers.
There are clear reasons why the bounceback dates are what they are, and why the UK gets a longer window consistently, and why they got restricted to Mods and up.
To quote Monty Python and the Life of Brian "Yes, yes, we're all individuals" - we need to treat each target group (bouncebackers, UK and North America general public) as individual (groups). Each has its particular nuances which means that the marketing plans aimed at them should be designed to maximize the benefit. Making them all the same doesn't do that.
Now, that doesn't answer why Public Free Dining last year was so short, but it does (at least) require us to look at all the factors involved this year to make a guess about the details of the '08 offer.