It's hardly a phenomenon limited to TomTom. If you're going to boycott them for that sort of trickery you might as well just stop buying things, everyone is at it one way or another.
It's still an improvement over their previous business model, which was effectively 'lifetime' too, except you had to buy every map update that was made available during the life of your device.
I don't really think they should be allowed to advertise 'lifetime' upgrades as a selling point if the 'lifetime' turns out to be whenever they decide to stop supporting the device.....
Lifetime at the very least should refer to the expected lifetime of a device.... At a minimum personally I would set the benchmark for this around 10 years for an electrical device.
Like is said its a totally ridiculous piece of circular logic. Tom tom another company to avoid.