Maybe because on the writeup on the app store ([URL="http://itunes.apple.com/us/app/find-my-iphone/id376101648?mt=8&at=10l3Vy]link[/URL]) says "If you misplace your iPhone, iPad, iPod touch, or Mac, the Find My iPhone app will let you use another iOS device to find it and protect your data. Simply install this free app on another iOS device, open it, and sign in with your Apple ID."
And I did specifically mention the "Find My iPhone" app.
I didn't realize that was built in to iOS now to locate it. Even though it's not built into Android, you can still locate it easily enough since you can install something like AndroidLost from the Play Store after you lose it and still find the phone. Not quite built in, but you don't have to proactively use something like this before losing the phone.