By your definition any system is modifiable because it can be modified after an arbitrary amount of effort. For example, it might require breaking a encryption key which takes years. But no matter, it is still *possible*, the only difference is the amount of time and effort it takes. Where do you draw the line?
Clearly such a definition is meaningless.
What matters is the intent. Does the device deliberately provide the user with the ability to service the software? A desktop PC running a standard desktop does. A desktop PC running kiosk software *does not*.
Granted, Jonno has posted some thoughtful arguments that modifying the actual device might not be strictly required in the legal sense for LGPL2. That is a line of reasoning that deserves serious consideration.