The McMurdo's price point is a real game changer. When SPOT was launched PLBs were typically out of the reach of the average public.

PLBs broadcast to the Cospas-Sarsat (sorry I wrote COSPAR earlier by mistake) satellites run by the USA/Eu/Russian governments - there is no charge for them.
Spot uses a commercial satellite phone system that they have to pay for.

The PLB satellites are more advanced in some ways, they are able to forward messages between each other, so if you broadcast a distress signal from the middle of the ocean it will reach base. SPOT can in theory transmit more complex messages, even voice calls if they wanted to fit the hardware, but the satellites are simple relays - the message is beamed down to a base station in the footprint of the same satellite. This means that their coverage in mid ocean or in the arctic isn't good.

Very low price PLBs might have a worse effect than SPOT. When they reach the price that every hiker and every car is fitted with them the system is going to grind under the strain - it was originally intended for ships/aircraft with professional crews and 'real' emergencies.

By having an operator, SPOT is able to do a little more triage on the message before alerting the authorities. Suppose SPOT were fitted to cars (like ON-STAR) so that a crash out of cell phone range could be detected. SPOT would be able to detect that eg. an airbag had deployed and inform local 911 rather than the PLB alerting the Coast Guard.

I'm not an apologist for SPOT - I personally would probably buy a McMurdo if I was going hiking in Alaska. But I don't think it's necessarily fair to think of them as only money grabbing opportunists.
If you regularly drive in winter in a remote area without cell phone coverage I can see the point of SPOT.