Clustered PK and Nonclustered Index on Same Column

I have come across several tables recently where the clustered PK on Column (X), for example, is also been duplicated as a nonclustered index. When I look at operational and usage DMV's for the indexes there are reads on the NCI. Why would SQL Server use a NCI to retrieve rows if it has a clustered PK that is on the same index? I would have expected the usage stats to have no reads at all. Did someone do this to prevent aggressive use of the clustered PK, ie. to prevent excessive locking on the clustered index?