I think you're confusing high definition (television resolution) with digital (broadcast signal). Of course, that's pretty understandable as most non-HDTVs do not have digital tuners to plug the antennae into.
In answer to your question, no. Antennae do not only work with HDTVs. They only work with TVs that have a digital TV tuner (ATSC) or with a digital to analog converter box to a TV without a digital TV tuner.
-Wolf sends