I don't think the IS-F stands for Flagship, F-Sport is Lexus' "sport tuned" division moniker meant to be like Mercedes' AMG or BMW's M. I'm not sure what the "F" is supposed to mean...bit I'd be surprised if its Flagship. In any event, the car is still an IS, and all the basic features of the car, the displays, the switchgear, etc are all carried over from the IS...which is the entry Lexus (well I suppose the CT is now), and there are for sure going to be feature differences between it and the LS, no matter how high end an IS it might be or how old the LS might be..
I didn't know that about the seek buttons also fast forwarding...I suppose theres always something new to be learned!