That, of course, is the key to the issue.
As with any engineering decision, it is a tradeoff.

Jez has obviously condidered all the issuses, requirements & constraints of his application and concluded that for his application iButton was not secure enough.
Only you know all the issuses, requirements & constraints of your application - so only you can determine whether iButton will be secure enough for your application.

However, what I can tell you is that your initial concerns about being able to provide multiple readers are unfounded - this is no problem at all with the Dallas 1-Wire^TM (or "Micro-LAN^TM") bus!