The 1880 works better because it has a built-in, low-noise amplifier. You can get clse to same performance if you add a RS 1171 cable amp or a CM 7775 preamp. Both are also very low-noise.
With digital signals, gain is less important than "directionability". There is plenty of gain provided by most antennas for the digital receiver to lock onto, even without an amp. This is true even down here, some sixty miles away. What gives digital receivers fits, however, is multi-path, which on an analog receiver shows ups as "ghosting" or multiple images. Low gain adds "snow" to the picture. Multipath is caused by signals bouncing off other large objects like mountains, buildings, etc., and arriving at your receiver at slightly different angles and times. If the receiver can't figure out which is the real signal and which is the "bounced" version, it loses lock and you get a blank screen.
The reason tha low-noise amp helps, to a point, is because it provides a bit better difference between the real signal and the multipath. Picture a graph with a "squiglly" line drawn where one Peak" is drawn a little higher than the others. It is clear to you which is the "tallest" peak but now move the graph across the room. It isn't so easy then. The low-noise amps are effectively bring the graph "closer". If you use an amp that generates too much noise, it can mask both the real and "bounced" signals. Picture a 3-year old coming in and drawing all over you nice graph.
What a directional antenna does is make the signals arriving directly in front of the antenna stronger than those arriving at different angles. Now, all of a sudden, the main peak on your graph got taller. Digital receivers like this very much. Again, since gain isn't as big a factor, almost any cheap antenna that provides a measure of directionability will work better than most of the less directional "bow-tie" designs.
You can drastically improve directionalbility, thereby reducing multi-path, by horizontally "stacking" two identical antennas in the same horizontal plane at some fraction of a wavelength apart (the math is in this thead somewhere but for mid-UHF frequencies, it works out to around 40 inches...) and then combining their outputs using identical length leads. This makes perfect sense, if you think about it, because now the only signals arriving directly in front of mid point of the two antennas will arrive at exactly the same time, thus staying in phase. This works for even the cheapest of the cheap UHF "Yagi-style" antennas, like the $22 RS 2160.
Originally, I had a monster 8-bay CM 4228 "bow-tie"-styled antenna installed off an upstairs deck, with a 7775 pre-amp. It worked very well and I got very high "numbers" on virtually all channels. The problem was that I would also get annoying dropouts everyday on most of those channels. Eventually I replaced this setup with a dual 2160 array and an 1171 amp. I now only get a dropout once every few months, and then only on certain channels.
The latest receiver designs have also made big improvements in handling multipath. I'm using a Sony HD200 and a Zenith HDV420 and both work a lot better than the E86 and 1st generation ATSC-only receivers. The next generation will be even better. The HDV420 works so well I can get away using two SS and an amp, or two 1880s sitting side-by-side, indoors in a loft area "looking" out a living room skylight/window towards Mt. Wilson.
Finally, probably the biggest single factor that has the greatest effect on performance is antenna location. You've got to move around and find the best "sweet spot". Sometimes just moving a few inches one way or another can make a huge difference, especially in attic installations.