There is nothing like a limited supply with a jailbreak.
As long as the download server manages the load, everybody who wants to get the software can get it 10 minutes after release.
People have been waiting for this jailbreak for months, so there's a high chance that they will have jailbroken their devices the night the jailbreak was released.
As the news that this jailbreak exists has been reported everywhere on the web, almost anyone interested in jailbreaking his device will know about it by now.
And they will have jailbroken their device the same day they learned about the JB.
So the 7 million jailbroken devices will most likely be owned the majority of people interested in jailbreaking their iOS 6 device, i doubt that there are still 50 million people out there who don't know about this JB yet or who did not apply it due to X...
So with 7-10 million people interested in Jailbreaking their iPhones, that may be a quite high number - but only if you ignore the 290 million other iPhones, iPads and iPod Touch out there that are NOT jailbroken by now and which most likely won't ever be jailbroken.
The majority of people owning iOS devices, 95+ percent, don't care for a jailbreak.
@NorEaster
The motivations of non-users are often difficult to evaluate, so the only real numbers we have about jailbroken devices are the ones from this article - and they are not that impressive if viewed in context.