The alerts are for huge catastrophes (a Presidential Alert), then for weather / natural calamities, and one for AMBER alerts. One can turn off the latter, but the Presidential alert cannot be turned off.
The article mentions only 4S and 5 get this update. That said, I have a 4 and it got the update this morning.
This was enacted in 2006, for those keeping track of such things.
I, for one, do not care for this any more than I like the idea of them reading my communications to begin with. Oh, I'm sorry, the "metadata" from my communications."