Las Vegas-area home prices retreated in January as measured by the influential Standard & Poor's Case-Shiller Home Price Indices issued today. After rising 0.2 percent on a month-to-month basis in December, prices in Las Vegas fell 0.5 percent in January, Standard & Poor's said today in its report. That compares to a monthly decline of 0.4 percent in prices among the 20 big U.S. cities analyzed monthly.