However, technology has since advanced to the point that someone could finally make the same measurements on our near and dear mammalian cousin, the long-suffering lab rat, and found--surprise!--different results.
The New Scientist article linked above gives a great account of the study, except for one glaring error: they say that axons are "each 1 millimetre in diameter in the giant squid."
No one, as far as I know, has ever voltage clamped axons from giant squid. They use giant axons from regular squid, and these giant axons can indeed reach 1 mm in diameter. But the common market squid that have been generously providing their axons to generations of neuroscientists--well, they're only about 10 cm long.