There is no direct linkage of those genes. They occur on the same chromosome, but that does not mean they are linked. Cream Legbars are single combed and have very blue eggs (at least mine do). It is now trivial to create a breed like Whitings if you want single combs and blue eggs, just start with a Legbar.
I prefer pea-type combs because they incur less frostbite concerns, but I imagine in warmer areas, they have the opposite view. My best blue egg layers are a sexlinked hybrid I create with a black Ameraucana (blue eggs and pea combs, both dominant) over California Grey pullets (single combs, white eggs, incredible egg producers). The only "problem" I have is they lay so much the blue fades to nearly white after a while, but I can live with that. Their phenotype is almost identical to a black Ameraucana pullet, but they are 100% sexable at hatch, unlike real Ameraucanas.