A few posts back (here), I made the point that biologists, unashamedly, establish biological processes based on a relatively small number of model organisms. This kind of argument, I noted, is regarded very suspiciously within linguistics where many (indeed, I would guess, most) practitioners consider it scientifically irresponsible to infer properties of UG based on the inspection of a handful of language particular Gs. I recently ran across a nice discussion of model organisms and their role in fundamental biology (see here). The most recent Nobel in bio was awarded for work on autophagy based on this process on brewer's yeast (here). The conclusions concerning the fundamental mechanisms are taken to be obviously relevant to biology in general despite its being based entirely on what takes place in yeast, a unicellular organism. In other words, what's good for yeast is good for humans, plants, insects despite their rather obvious differences.
The assumptions behind the logic of model organisms and the biological inferences it licenses is embodied in the featured quote by Jacques Monod that heads the linked to paper: "Anything found to be true of E.coli must also be true of elephants." Read this again. And again. Now translate this into the linguistic analogue (anything true of English must be true of Swahili). Does it sound natural to you? I would bet not. Within linguistics it is, I think, widely assumed that the only legit way to establish universals is bottom up, by generalizing over the properties of Gs. This is why linguists are so defensive when someone remarks that GGers only study English. Of course this is false, and that is worth pointing out. But the reflexive riposte (i.e. that GGers DO study TONS of non Indo-European languages and have FOR A VERY LONG TIME) is evidence that GGers believe that were the criticism accurate then this would be scientifically shameful.
It is curious (and important) that biologists don't feel the same way. In fact, the opposite. But so far as I can tell, the logic is the same: the fundamental principles of G organization will not and should not differ across various Gs. Why not? Because these are rooted in biologically general properties that guide human linguistic facility. We should expect conclusions drawn about UG in English to generalize to all other Gs. The only serious impediment is being misled by the surface idiosyncrasies of English (or whatever other G one is studying). And that's where PoS arguments come in. They are useful precisely because they attempt to establish UG principles by abstracting away from the surface noise that PLD can induce.
Does this make such arguments infallible? No. Does this mean that cross G study of typologically diverse Gs is of marginal utility? No. What it means for me is that the reflexive suspicion that contemporary GGers have for PoS arguments of reasoning from the properties of a small set of Gs to general properties of FL/UG is methodologically misplaced. Or, more accurately, if it is suspect in linguistics then it is also dubious in biology. And those that believe this should contact the Nobel committee before it errs again in supporting scientific malpractice.