With all of the data the Blizzard has at its fingertips it's possible that they actually see fire and frost DPS as relatively close. Consider that they could have access to the amount of DPS done by every character for every encounter since the expansion was released. Also consider that there are a lot of really bad players who will manage to do substandard DPS even with a good spec. Fire spec isn't exactly hard to play, but there are enough nuances that you can wind up with suboptimal DPS with sloppy play. Average out the DPS over thousands of mages and encounters and it's possible that Blizzard sees the two as being within some margin of error.
Since EJ theory crafting always works under the assumption that the player will be good and play the class as perfectly as possible, we only bother to look at the theoretical DPS that the class can output. In this case there's a noticeable disparity between fire and frost. It's possible that the developers are now aware of this difference and have decided the two specs are not as equal as they had believed them to be based upon any data they might have. It's also conceivable that of the 3.1 changes announced so far they feel as though fire is pulling farther ahead based on the addition of the living bomb glyph and the scalability of deep fire.
It's highly speculative on my part, but based on a large number of blue posts on the Blizzard forums, the developers claim that they have access to the kind of information on which I'm basing my assumption. I think that most people here would agree that frost is comparably easier to play than fire or at least more straightforward, which means that the average mage can get more out of it than they would be able to with another, more complicated spec. It's possible that in the hands of the unskilled masses, the two specs produce DPS numbers which are not significantly different statistically based on the data Blizzard has amassed.
The problem is we told Blizzard Frost Raid DPS was too low in WOTLK beta. We were right, once again, and they were wrong, once again. We have a pattern of them telling those in beta/ptr that they are wrong and those sources being proven right in live over and over again. Of course there are those individuals making wild claims but man, many people provided the numbers. I was a long time Frost mage but I could not help but move to FFB when considering the Frostbolt glyph removes a defining feature of being Frost for me while FFB spec retains that feature and also much higher personal and raid DPS.
Granted Frost AoE is higher but not enough to warrant bringing a Frostie on a difficult boss fight with an enrage timer where speed counts.