Should be the opposite. All full-service, full-power stations should remain so. Some full-service stations are broadcasting in DTV at lower power now by Special Temporary Authorization (STA), mostly those going back to their old analog channel for DTV, but come 2009, all stations will either have to replicate their current analog coverage, or maximize facilities, which in some cases, means that the station will have more coverage. In any case, full-service DTV stations should not have less coverage than they do now.
As for LPTV stations, they are limited at this time to replication, due to a freeze in applications for strengthening facilities. As usual, there are always exceptions for special cases, in which STAs are issued, but once the freeze is lifted, expect a lot of LPTV stations to maximize facilities. LPTV power limits for DTV are 10% of that for analog, or 300 W for VHF and 15 kW for UHF. Over-the-air viewers at the fringes of the coverage areas may find themselves not getting a LPTV station they once got, but viewers well within the coverage areas will in many cases see a clearer signal.
One hair to split: don't confuse DTV with HDTV. Full-service stations will be required to go to DTV in 2009, but not necessarily HDTV. DTV is standard-definition digital as opposed to HDTV, which is high-definition digital. Some networks, such as Univision and TBN, are choosing to use their bandwidth to air multiple programming streams in standard def (TBN will have five), rather than one stream in hi-def and the others in standard def.