"multiple 'native' apps for various products is [...] unmanageable."
I think that was the one main reason for FT.
With iOS, Android, RIM Playbook and now WebOS to support of course a web interface makes much more sense.
Sure it's costly to develop HTML5 systems since the tools are still a bit lacking,but they'll pay that off in a couple of years of not having to support all those platforms natively.
It's not like they would benefit greatly from a native app anyway, since a newspaper doesn't need major interactivity or 3D graphics. The less gimmicks the better. Publishing information is what the Web was made for.