It was already known that Apple would shut the signing window once it released iOS 7. Those looking to downgrade iOS 6.1.3/6.1.4 are now out of luck as these firmwares are no longer being signed.
Anyone who either wanted to downgrade from iOS 7.0 to the aforementioned versions or from iOS 6.1.4 to iOS 6.1.3 would have needed the signing window to be open. Users who have not yet saved the SHSH blobs for these firmwares on their device can no longer do so, since Apple’s servers won’t authenticate a restore onto iOS 6.1.3 and iOS 6.1.4.
Earlier this week Apple released iOS 7 to the public. It was initially believed that the signing window for the previous firmwares might be closed within hours. However, that didn’t happen. The company took nearly three days to do that, thus leaving ample time for customers who were the first to upgrade to iOS 7, to go back down to those firmwares if they wanted to do so. One might think why customers would want to retain an old firmware when a new, much better one if already out. The simple answer here is the possibility of a jailbreak. Developers are currently working on an untethered iOS 6.1.3/6.1.4 jailbreak and there’s hope that a release might take place in the coming weeks.
So those who want a jailbreak but have missed out on the opportunity to downgrade iOS 6.1.3/6.1.4 will now be stuck on iOS 7. Nevertheless, there might be hope for them as well, given that work on iOS 7 jailbreak is already underway.