The S2.1 series release notes discuss the move to a Dojo tag plugin and the Ajax tag documentation includes the same information. As has been noted by others here on JavaRanch, RoseIndia isn't always your best bet for reliable, current information.
RoseIndia seems to come up with a lot of examples in google. Either way I'm still having trouble with the datetimepicker. The code compiles and runs, but it doesn't do much, as in, I see "Enter Date:" but that's about it. What other config do I need to add/install to make it work?