A new day on MacRumors forum, but same old s*** - "Apple not allowing downgrade..."
I wonder if this argument has been ongoing since the birth of MR....
Well, it's been going on since the iPhone 3Gs with the new bootrom. Before that, you could easily downgrade in iTunes using a downloaded IPSW file. No biggie. Then they changed how iBoot works after about November 2009.
For example, my iPod touch 2G (2008 MB model) can easily be downgraded from iOS 4.2.1 to 3.1.2 or 2.2.1 or whatever else I have downloaded without needing to check for a signature. Even offline.
After the new bootrom 3Gs devices checked for a signature. BUT there were SHSH blobs that you could use when you jailbroke your device and it saved them to Cydia, or you saved them yourself with a utility like tinyumbrella. Example 2, my iPod touch 4th gen with the A4 chip had iOS 6.1.2 on it for a while and I got tired of how laggy it was, so I used my SHSH blobs from iOS 4.2.1 and restored it. It was soo much faster and I was much happier with it. The apps I used still worked on it and there weren't that many to begin with. I used it mostly for music, and the battery lasted longer on 4.2.1 too. Video example: iPod touch 4G speed test
Then the A5 devices came out and SHSH blobs really didn't do much for them. The rest is history.
So, yeah. Since late 2009, it's been much of the same.