The WRT54G Router is something of a novelty as the firmware is Linux-based and open source. Unfortunately, recent versions of this model have a closed source firmware based on VxWorks. Hackers are calling foul - why go back on such a great thing?
The relationship between hardware and software vendors has always been interesting. Sometimes they "coopt-lude" so well that they Juggernaut; Wintel, for example, comes to mind. Other times it's nothing but the rawest form of power, pure reward and punish behavior. I once owned a Dell that could run nothing except Windows 98, because that was the only driver that the NIC supported. It keeps you locked in to the same set of vendors, and it keeps you locked down from too much horsing around.
There has been a few interesting hardware companies, such as Roomba, that have made interfaces to their operating systems available and opened them up. (Incidentally, I went to high school with one of the founders.) I wonder if we will see more of this? Imagine an open source washing machine where you could modify the code to do what you wanted it to, maybe some specialized cleaning job like washing loads of sneakers, or maybe for a different use entirely. It's a pretty exciting idea.