I do have some problems with this, though:
In practise we never end up walking the design tree forever. Residue from our past mistakes (the dotted nodes) lingers in the codebase and makes it ever harder for us to walk around the design tree. Eventually, fresh competitors will be able to do it quicker and take our users.
I mean, is this really the case? Maybe it is if you work with smartphone apps, but apart from that, I cannot really think of an example not only in my own niche (administrative systems in mid-to-large companies, so ERPs, Reservation systems etc.) but also in terms of things that I never worked on, but I use regularly.
E.g.: Google took out all their attempts at creating a social network (I remember Orkut and Google+, probably there were others). They were the competitors (to Facebook) and no matter how "nimble" they were in adding or changing features, in the end they just quit.
Word/Office is probably another classica example of something that has lots of "design decisions" layered like geological strata, but they are still dominating the market (I am Mac User, btw, so I am not talking of Open Office as a "innovative alternative", here.)
The authors seems to think that customers can't wait to get rid of, I dunno, Oracle Finance, as soon as someone comes in with more feature... in my experience the reality is that no matter how much they hate the old workhorse, having to convert lots of existing data (and adapt processes, and retrain personnel) is a cost which is very difficult to justify, and no amount of "shiny new features" will really be the main driving force in such decisions.