rob, the difference I believe is that the GRA has that right as an Achron. (BTW, the GRA is often considered on the level of a Rishon.) We (you and I) don’t have that right as being (relatively) a nobody. Yes, I understand your point about the Rishon-Achron aspect (also see my point about the GRA being considered a Rishon in many respects), but we are nothing of anything to argue with any Rishon or Achron.
squeak, my intention isn’t to play one or both sides of the issue, but rather to quote Rishonim/Achronim in the matters of scientific infallibility and secondarily the GRA’s commentary on the Rambam. I’m not offering my own chiddushim here. (At least not intentionally.) How you reconcile the Rema (I quoted) with the GRA (I quoted) isn’t something I discussed here nor something I feel compelled to currently explore. In any event, I wasn’t discussing the infallibility of Rishonim in matters of Torah or science (perhaps another discussion for another time) but rather Chazal’s infallibility, as described in the meforshim.