Where is the official word that this is a US update? Just because MacRumors posted it?
There is no official word. Someone just found the European restore file and people took that as the "release".
For those that are unsure if the update is legit, go to
http://itunes.com/version and you will see all the URLs for downloading these files. Apple uses Akamai's edgesuite.net for all the downloads. Also notice the URL it forwards you to.
iTunes updates work by suggesting a version as the newest based on what you are currently running. Below is all the builds known by iTunes and what version you will be asked to update to if you are running that build.
1A543a -> 3A109a (1.1.1)
1C25 -> 3A109a (1.1.1)
1C27 -> 3A109a (1.1.1)
1C28 -> 3A109a (1.1.1)
3A101a -> 3A109a (1.1.1)
3A109a -> 3A109a (1.1.1)
3B48a -> 3B48b (1.1.2)
3B48b -> 3B48b (1.1.2)
Unknown -> 3B48b (1.1.2)
This tells us that all iPhones that are not currently running 1.1.2 should be updated to 1.1.1. Also, if your phone is hosed and it can't figure out the version you are currently running, you get 1.1.2. For that reason I do not think it is bad for US phones to run 1.1.2.
It seems obvious that Apple does not intend to release 1.1.2 to US iPhones just yet, or even at all officially though iTunes. If they do not, I suspect another update is coming very soon.