This protective layer is deliberately restrictive, which is good for consumers. After all, who wants to buy a device, with a dedicated purpose in mind, but have it crash or be cumbersome to use? Yet, for hardware hackers, eking out versatility is an extra sweet result due to the effort needed to circumvent the layer protecting its hardware.
Many may ask why would you want to do something like this anyway. For most the question is moot; simply being able to prove you can is sufficient motivation. Others put forth practical applications - for instance, outputting GPS locations via Bluetooth to a WiFi-enabled laptop, thus pinpointing precisely where open WiFi networks are located. And others imagined how nifty a tiny touchscreen media player could be, particularly with its built-in SD slot and loudspeaker.
The key to it all is Linux. The TomTom GO runs Linux, specifically a custom distro called TomTomLinux or TTL, with an ARM processor. So, logic dictates, if you can compile a program for Linux on the ARM then you can run it on the TomTom.