Why does Facebook not show "via iPhone" when you update your status from your iPhone anymore?

I doubt it's anything quite so insidious as a falling out between Facebook and Apple.   More likely it's either a sign that Facebook is moving away from app-specific designators (the Android version has also dropped it). It could also be that the same Facebook app can now be used on the iPad and iPod touch, so it's easier to omit it than to try to figure out which device the user is posting from.  Not that identifying the device is really that difficult, but it may be something the developers couldn't be bothered to deal with.

They used to have "via mobile", "via Facebook for Blackberry", "via Facebook for Android", etc as well.  I think the original purpose of these little tags was to demonstrate to non-mobile users that yes, you can use Facebook on your mobile.  Now that smartphones are ubiquitous, I suspect they eliminated it simply to cut down on clutter.  As far as I know, FB and Apple get along fine; they are not direct competitors.

Go to the settings, click on Facebook (below Twitter it should be  there). In this put in all the required details and then click done. It  shall save your information. Now exit the settings and drag the  notification center down. Here beside "Tap to tweet" you should see "Tap  to post". Now whenever you want to update your status use this Tap to  post option and you'll be able to see "Via iOS" with every post you do  using this method.

Facebook is movomg away from hardware specific labeling- they see it as advertising for apple and android when the facebook experience is what they are trying to show- fluidity cross platform.