Facebook is developed by hundreds of people and has near unlimited resources for feature development. Facebook have Joe Hewitt – a very experienced Objective C and Cocoa developer – to lead the Facebook for iPhone team, and he will be continuing to expand the breadth of the app as time goes on.
Fluther, on the other hand, is created and maintained by just three guys, and although they are extremely skilled web developers, none of them to my knowledge is a Mac developer, nevermind an iPhone developer. They would have to outsource the work to someone who can develop on that platform, and that costs money and is distracting to the other more important core application efforts – like the API – that they are working on.
Give the guys some time to work on the things that need to be done first, and hopefully the less necessary features, like a native iPhone app will follow eventually. Fluther is still quite new and quite small, and although it would be amazing to see features pop out all over the place, take a look at the amazing community we have here and keep your eye on what matters.
Oh, and I recommend this for reading:
http://www.37signals.com/svn/archives2/revealing_hidden_assumptions_in_estimation.php