This was part of the confusion over ‘digital antennas.’ There was a common misconception that HD would be exclusively in the UHF band and that just isn't the case. There may indeed be ‘tweaks’ to certain antennas that ‘may’ do something to improve reception, I'm not qualified to argue that point. However, it likely has nothing to do with digital or HD per se. The old analog system (NTSC) and the new digital system (ATSC) still use the same frequencies, though some channels went away to make room for cellular.
If you get a “digital’ (or any) antenna, that is limited to UHF (400-700 MHz), otherwise known as channels 14 - 51, you will be disappointed if you have VHF stations, channels 2 - 13, in your market. There is a difference between VHF and UHF antennas and you need both or a combo if you have a VHF station in your market that you want to receive.
To make matters more complex, we have virtual channels now. This is where the station goes by its historical channel number, but its new digital channel is another number. Your TV generally figures this out automatically, but one of the those numbers may be in the VHF range and the other in the UHF range and the distinction is important if your antenna only works well with UHF.
http://www.stationindex.com/tv/ can help you identify the virtual and actual channels in use in your market.
To sum up, don't focus on ‘digital’ or HD, but determine whether you need VHF in addition to UHF.