What we needed was a two-episode arc in a prospective fifth season of Enterprise, to explain this inconsistency!
I ultimately do rationalize it as most do--Romulan foreheads are to the Vulcan genome what an epicanthal fold is to the human one, a trait shared by many but not all. Now the morphological gulf between giant creases of bone and the precise construction of an eyelid is large, but at that point I can comfortably suspend disbelief.
As for the Remans, I assume they're the result of two thousand years of living in mildly radioactive caves. This is of course not ultra-scientific, but it's more fun to assume they're Vulcan, genetically. Their paleness could be attributed to simple lack of UV light (melanin production must be stimulated in Vulcans as well as humans). The curiously missing inner eyelid function which protects Vulcans (and presumably Romulans) from bright light might yield to the same principle, that without exposure, the specialized cells which produce polarizing compounds simply don't develop normally.
Apropos of nothing, one of my biggest beefs with how Trek dealt with the Romulans was the ridigity of their society, particularly a throwaway line in Inter Arma Enim Silent Leges, when Garak regales Bashir with the "grayness" of life on Romulus. If you're just going to wind up boring, why bother leaving Vulcan?