I agree. Like spin welding that uses friction to melt the plastic parts or ultrasonic welding plastic parts together, again using friction to generate the heat, the plastic is the same compound in both cases.
One more thing, welding soldering or whatever you want to call it, the process only works for thermoplastics, plastics that can be melted with heat, not thermoset plastics which are essentially two part epoxy like plastics. For those you have to glue and/or use mechanical fasteners to reattach as they will just burn when you attempt to add heat after they have already set.
Some plastics, like acrylics, are also easy to bond using solvents like acetone. Just put the parts together then flow the solvent into the junction and allow it to setup while the solvent evaporates.