Regarding my noting that, "Chloramine is presumably a strongly charged and reactive salt, easIer for the RO and DI filters to remove:" Upon further looking, this is correct, yes it is easy for DI (activated carbon/charcoal) filters to remove, but chloramines in tap water can quickly clog, fill all the binding sites of standard filters. The chloramine-specific filters simply contain more activated carbon - either more active/concentrated or more packed into the filter, so they last significantly longer.
