What country in western Europe ? Never heard about anyone talking about a dual-sim telephones in France. But there is not much point of having two subscription to two companies that prices are aligned.
Portugal. The reason I have one is because I have a company-issued SIM card, besides my personal one. But here prices are not actually aligned, since some providers have free, unlimited calls between members of the same plan, but not between members of different providers.
Wiko Mobile is a big name in France (#3 in 2013) and (almost?) all the smartphone they sell are dual sim:
http://world.wikomobile.com/p-Wiko-Smartphones
they are sold in supermarket as well (Auchan etc..)