You should also be able to see the speed of the blades (or a multiple depending on how the motor is wound) in the back-emf produced by the motor and fed back out the power cord. I've seen many cases where a sewing machine would produce frequencies that interfered with the horizontal and vertical sync of a television set ... in principle, a blender motor should als be noisy.
The simplest way to test this would be to connect an oscilloscope or spectrum analyzer to the AC power line. This can be dangerous, so I'd recommend capacitive-coupling or for an even safer test, inductive coupling. Capacitors are effective high-pass filters, so picking the correct value will reject the 60Hz power while letting you see the high frequencies produced by the blender.
That reminded me of something I have wondered about for a while, I was playing an Atari video game as a kid and the picture quality massively degraded. After a death I went to mess with the cable and found it unplugged, but the game was still somewhat visible. While I never could reproduce the effect I assumed it was probably going though the power lines and not EM. Any thoughts?
PS: I assume the simple nature of the graphics made a difference but that's about it.
An small air gap is generally capacitive and will pass the higher frequencies while rejecting the lower ones. In the old days (when we only had a few channels on cable television), the CATV systems had a lot more loss and ingress (60Hz from the AC and other signals induced onto the center conductor). To support the higher frequencies now used, the cable has to be carefully installed and maintained.
In the '80's we could get full cable TV by pointing a large Yagi antenna at a particularly strong "leak".
What makes you think that TVs receive video signal through the power line? An apartment I was staying in a few weeks ago had terrible cable signal to the TV, whether or not the coaxial cable was connected, but careful arrangement of the cord produced better signal while unplugged than haphazard arrangement while plugged in. Cables are waveguides. I'm surprised you couldn't reproduce the effect.
The simplest way to test this would be to connect an oscilloscope or spectrum analyzer to the AC power line. This can be dangerous, so I'd recommend capacitive-coupling or for an even safer test, inductive coupling. Capacitors are effective high-pass filters, so picking the correct value will reject the 60Hz power while letting you see the high frequencies produced by the blender.