As far as I understand, Data Replicator is a back-up program, to frequently back-up data from your PC's to the NAS and keep stuff like mail, my documents, pictures and other data you don't want to lose, safe in case something happens to the data on the PC.
Cloud Station is more to share data between several PC's (or tablets etc) like DropBox. Every time people with access to your Cloud change, add or delete a document, the application synchronizes the contents on the NAS to ensure everybody gets to see the latest version.
So, they serve a different purpose. I wouldn't want to sync my mail database every time I send or receive a mail. A backup every couple of days is enough ...
NAS : DS212j with 2 ST2000DL003 in SHR / DSM 4.2-3211
LAN : Fritz!Box 7170, 4 Devolo, 1 Icidu 200Mbps AV homeplugs, 2 5-port switches
HW : Conceptronic CHD3NET, ACRyan Playon!HD, Eminent EM7075dts, Wii U, PS2