No, not everyone living in the lowcountry has flood, wind and hail insurance. However, in the areas you'd mentioned, only Goose Creek has more areas oustide of a mandatory flood plain than inside. Most parts of James Island, John's Island, and many parts of West Ashley are in federally designated flood plains that will require flood insurance. Many parts of James Island as well, are in wind zones that will require mandatory wind&hail coverage.
South Carolina Wind and Hail Underwriting Association and
FloodSmart.org | Flood Smart | Watches | Tornado | Weather are certainly great sites to visit. Insurance rates, however, are on a house-by-house basis. Insurance ratings not only take into consideration the location of the home, the elevation/construction of the home, but it's prior claim history, your prior claim history and your credit rating, among other factors.
Checking with a couple local insurance carriers for each specific home you're interested in, would be the best and only way to get a solid idea of what your insurance payments would be like.