My bet is that QA is either not, or perhaps too tightly, integrated with engineering. They either received a push back when they reported the implementation stinks or they passed it "as designed" ignoring the fact it was poorly/incorrectly designed.

By and large, Tom Tom software kind of sucks. To be fair, I only have experience with their PDA software, but the screenshots I've seen of their dedicated hardware seem to indicate the software is the same.

I think it's a real shame that Google didn't buy either Telenav (acquired by Tom Tom) or Navteq (acquired by Nokia). They're pretty much the two biggest map providers and the situation for the GPS market could take a bleak turn when/if licensing fees skyrocket.