Earlier quoted context omitted.
This is Apple themselves recognizing that hardware that is too old to run iOS7 is still useful.
Nah, this is because of the new 64 processors. There's still no mechanism that allows for 64 bit iOS7/32 bit iOS6 fat binaries, it's either 64 bits iOS7/32 bits iOS7, or iOS 6 only. Probably the first time that apps compiled for the latest and greatest can't run on old phones at all.
iOS 7 is 64-bit only on the iPhone 5S.
iPhone 5S will run 64 bit iOS 7 and can run both 32 bit and 64 bit applications.
iPhone 5C, iPhone 5, iPhone 4S, iPhone 4, iPad 4, iPad 3 (or whatever they are called), iPad 2 and the iPad mini all will run 32 bit iOS 7 (kernel, libraries, drivers and the Applications themselves).