The remainder of those channels are sparsely populated.
Check your local listings and see how many channels you can receive above channel 51 as they are the only ones desired for mobile broadband.
Bzzt. Though the magic of virtual channels, the actual channel number for the digital channel is hidden. For example, in the Lansing market
6 = 59
10 = 57
18 = 34
23 = 55
47 = 38
53 = 51
To a guide it might look like there is only one channel in the 52 though 69, but actually there are 4 using those frequencies (one analog, three digital). Under current law, stations in 52 - 69 need to leave the frequencies after 2/17/09