> That Android app will run on hardware that's many years old though, thanks to those extra dev resources.
Huh? They said they started off with 4.0 support, and then dropped it, moving to 4.1 support. Android 4.0 came out in late 2011, and 4.1 came out in mid 2012. By simply supporting iOS 7, on the other hand, they would be able to support everything back to the iPhone 4, which came out in mid 2010, over a year before Android 4.0.
WhatsApp currently can run on J2ME phones, but won't run older iDevices thanks to the way Apple runs the app-store.