His point, which you apparently missed, is that tab is normally used to evaluate identifiers. Changing it as you suggest would cause problems when evaluating identifiers with properties.
Then simply make it complete only when the period comes after a space, or when it's the first char of the sentence. But that would be useful only if the reasons behind this are about not being able to complete nicks followed by the '.' mode char. And I don't know if that really happens.. this is only a guess.
