Blob banter
Those of you with jailbroken iPhone3G and ipt2G devices may now have noticed Cydia starting to save your SHSH blobs too, just like it does for iPhone3GS, ipt3G and later devices. Thats because starting with 4.0, Apple started putting a soft SHSH blob check in the firmware. The SHSH blob check is very real in the sense that if iTunes cant get your blobs (because the Apple signing window has closed), the iTunes restore will error out. But its soft in the sense that those devices can always use redsn0w or PwnageTool to get past the error (the bootroms themselves for those devices dont require blobs to be in the firmware files, unlike the newer bootroms).
Furthermore, since the 3.x IPSWs for these devices dont enforce it, you can always restore to 3.x IPSWs outside of any signing windows.
So, Cydia is doing this to allow you to continue to use iTunes to restore to 4.x on iPhone3G and ipt2g outside of Apples signing window without needing to use redsn0w or PwnageTool to get around Apples annoying new restriction.