Very nice data, @MachoDrone, thank you for this post!
I had taken some similar measurements a year and a half ago, when I got my first HS300. I used Kill A Watt model P4400, which is similar to yours but reports just one decimal instead of two. At that time I found that each plug turned on added 0.6W, and I did not detect the baseline usage at all. This result is a little different than yours, so I was inspired to repeat my measurements.
Instead of the Kill A Watt I used before, I decided to use a smart plug. @kevin1 found that they are precise to a very small fraction of a watt, see his post Data Science of "On", "Off" and "Standby": II - #5 by kevin1.
When I measured energy usage in this way, I found that instead of a static number, the value was constantly changing. I don’t remember my Kill A Watt jumping around like that. To dig a little deeper, I plotted the value over time. My measurement technique for recording from the Kasa app is described in the post Data Science of "On", "Off" and "Standby": II - #4 by jefflayman.
The results above are one minute’s worth of data for the blue line, and a second minute’s worth for the orange line. The average of each series is also plotted as a horizontal dotted line. I could discern no pattern in the variability, but in general my result is near 1⅓ W while off and 2W while on. These values agree well with what you measured.
I do not own a WeMo, so could not compare to your data there. I do have the KP115, so I repeated the above measurement on it. I watched it for a while in addition to these recorded measurements, and continued to see spikes well outside the general trend, so apparently the KP-115 just has more scatter. The good news is that the average energy usage is less than the HS110: I would call it 0.6W while off and 1.2W while on.
Of course I also repeated the measurement on the HS300. Results are shown in the chart above, where the colored lines indicate how many plugs are turned on. Variability was much like the HS110, and averages were close to your measurements.
My HS300 hardware does have the USB sockets, so that may account for the slight variation present. I don’t know how to pull out the firmware version number, but the Kasa app reports “No Updates Available” so at least it is current. My HS110 is like yours in that it does not have a USB socket.