Going through the source code for WindowManager, it seems that the title isn't actually used anywhere, except in the debug and parcel writing methods.
Furthermore, searching google for +"windowmanager.layoutparams" +".setTitle()" site:grepcode.com
doesn't seem to return any results where the setTitle() and getTitle() methods of WindowManager.LayoutParams
are actually used in production code.
I'd say that the Android engineers felt that maybe at some point of time in the future they might need a title property, and put it in as a stub.