Hi Seema,
yes, business content info objects exists in multiple catalogs , not only this objects, there are couple of other info objects from FI area exists in more than one catalog (ex : 0gl_account, 0comp_code..etc).
this is just to have grouping of objects in each catalog, as these objects exists in all these ( AR, AP and ,GL) modules. see sap help on 'catalogs creation"
however custom info object can't be assigned to multiple catalogs.