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You have to remember that DTV is also all about efficiency of spectrum usage. The FCC is currently trying to squeeze back the TV spectrum further.
The DTV transition in 2009 reduced the TV broadcast spectrum from 68 to 50 channels. The current of round of discussion in Congress is about reducing that further to 30. This means that terrestrial free to air TV is under threat and DTV with the ability to squeeze multiple streams into a single 6MHz terrestrial channel is seen by many legislators as a panacea.
Most cable companies have severely curtailed analog or discontinued it already. All new TVs have cable ready tuners.
Consider this: terrestrial DTV broadcast via 8VSB modulation over a 6MHz channel with an audio/video payload of aboout 18.5Mb/s, can carry five SD (better than NTSC) streams or up to two HD streams in one terrestrial channel.
Digital cable distributed over the same 6MHz bandwidth uses 256QAM modulation with a net video/audio payload of about 37Mb/s. It can carry up to 12 SD (better than one NTSC) streams or up to 4 HD streams over the same 6MHz channel which would carry an NTSC analog signal! (Cable DTV is via a more benign distribution environment of a wire as opposed to terrestrial over the air, which accounts for the extra program streams in one six MHz channel),
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