Iron blocks are usually sandcast in a cast iron alloy. In this way there are no need for liners. In an aluminum block liners must be used, or the cylinderwalls must be coated with Nikasil or similar. Wet liners are prefered before dry liners, and this creates a problem between the steel liner and aluminum block since the aluminum expands more than the steel. The latest is however coated ultra thin AlMC liners in an AlMC block, these are however very expensive.
Cast iron is a very good block material, the only downside is the weight. BMW even used cast iron blocks in F1 during the eighties.