* The Voyager non-humans looked really.. well.. HUMAN. Kes might as well have been a chick I dated in highschool, Tuvok looks more human than vulcan, B'Lanna is like Meg Griffin with a head injury (look at her compared to Kaylar)
B'Elanna's father was Human while her mother was Klingon.
K'Ehleyr's father was Klingon. As you can guess, her mother was Human.
In genetics, that can make a difference in how prominent a trait or two turn out. The development of the cranial ridges in Klingons be more expressed through the male sex chromosomes or other traits passed down from the father. It would explain why B'Elanna had ridges like that.
P.S. At least several Vulcans before Voyager came out looked a lot more Human than Tuvok did...