Many of the stations that were broadcasting on L-VHF before the digital transition did move to UHF or H-VHF, but not all. The L-VHF band remains... I think in part, because the cell phone / PCS providers don't what it as badly as the UHF spectrum.
There are issues with noise in the L-VHF band that make it necessary to use a larger antenna than you might expect. In your case, WPVI appears to be your best opportunity for reception of an ABC affiliate, and the signal strength is high enough to give you a good shot at reliable reception. Still, your best results will be with an outdoor mounted antenna that is designed to receive L-VHF channels. Much of the noise that troubles the L-VHF band is generated by electrical and electronic devises... which the typical home is filled with. So, attic mounting will likely place the antenna close to interference generating devises while blocking some of the desired TV signal.
http://forum.tvfool.com/showthread.php?t=2858
http://forum.tvfool.com/showthread.php?t=109