Bold added to show where the logic of this argument breaks down. By analogy, one might say "Locks and policeman are worthless in preventing burglary; because an effective burglar will overcome them." An effective burglar being defined, for the purposes of TA's argument, as someone capable of overcoming locks and guards! The point is that locks and similar security devices alter the effort-reward ratio of an attack.*
This the most basic thing to understand about the economics and psychology of security, and variants of TA's argument above have been repeated throughout the thread without anyone being willing to come to grips with the answer: all security is about raising the effort barrier to attackers.
With Android (sandbox virtual machine) and Symbian (privilege and certification system), or even a decently configured Windows system (firewalls and virus checkers with daily updates) this barrier is enormously higher than for the Nit. In fact, Nokia don't seem to have thought about security at all with the Nit - and it should have been the starting point and key feature for a consumer device designed for accessing the Internet.
Of course, Nokia haven't been alone in their mistakes. Apple have made exactly the same errors with the iPhone, and are now rushing to correct them:
Shutting down a firewall - especially on a system with decent anti virus and malware - is not easy.
It's much harder than merely adding a keylogger to a PIM; if its doable at all it will probably only be because of a temporary vulnerability that will get patched before 999 in 1000 attackers have a chance to use it. By comparison, the Nit is a house with no locks on its doors and a big "Come on in!" sign.