At this point we're getting more into philosophy than anything else. But if we consider "pilosophy" to be a subset of "calling the cat a bastard," then I guess it's appropriate for the HabitableZone... :-)

In the absence of physically testable predictions, many string theorists have resorted to arguing that, since physics is reducible to mathematics, it is the mathematical viability of a theory which should prove its ultimate merit. I think you're entirely correct in questioning the underlying presumption that physics is reducible to mathematics, but I don't believe that it necessarily goes the other way around, either.

The problem with deeming something to be a "Theory of Everything" is that "Everything" is an awfully broad territory, encompassing much more than physical reality. Mathematics is probably the most solid example of this. The square root of negative one, for example, can have absolutely no basis in physical reality, but it is nonetheless real -- just not in the same ontological sense as dirt or quarks. Another (much more poorly understood) example would be consciousness itself. Although it is popular to believe that consciousness is a byproduct of physics -- since it can be easily manipulated by effecting physical changes to the brain -- I personally believe that it is a separate phenomina which manifests through, and is limited by, physical reality, but is not fundamentally reducible to physically reality. Much in the same way that mathematics manifests through, and is limited by, the minds of mathematicians, but has its own reality independent of those minds. In my personal philosophy, it is the interplay of these three irreducible realities which creates "everything" -- inclusive of phenomena such as self-emergent complex systems (aka "life"), and also love, politics, et cetera, which something like string theory would totally fail to account for.

If my philosophy described above -- the cosmos as the product of three irreducible realities -- seems more like faith (or philosophy at best) than science, then that's a fair criticism. However, that's the field that a true "Theory of Everything" must play on, and the string theorists' presumption that everything is reducible to mathematics is no less a statement of faith. If they're not prepared to argue that point in philosophical terms, then there's hardly any point in arguing with them at all.

Cheers,

Nathan.