No misunderstanding at all. I realised you weren't being specific to TomTom, but I was a little concerned that TomTom owners might follow your advice.
It's probably safer to buy for other products, but TomTom have their system (well the 'GO' range, at least) pretty tightly sewn up with product codes and activation codes. Each unit and each map has a unique code, and only TomTom can generate an activation code to pair them. Once they've done that, they'll refuse to produce activation codes for the same map unless there are exceptional circumstances.
The "Western Europe" con might work on other units too, with people offering the full maps, but then delivering the 'major routes' version instead.
When it comes to software of any description (including DVD videos) I'm very wary of
. There's a lot of people passing off copies as the genuine article. If you're going to part with hard cash, then make sure you're getting the real thing.