I was thinking principally of the sheer number of man years that have been put into the system. I know that's not a very accurate yardstick, hence the smiley. :o)
My understanding is that the technology Powerset got from Xerox is a production quality, multiple language parsing system with a language-independent core, with the long development time being due to the engineers being allowed to work on the problem until they had solved it to their satisfaction.
Of course, all of my information comes from the above-mentioned presentation, so a large pinch of salt is almost certainly required. :o)
PARC has certainly done brilliant,pioneering work in many areas. What most people miss is that PARC had many deadwood/unsuccessful projects (and people and worthless papers ) in its time.
I know nothing about what exactly PARC licensed to Powerset, but without more data, I wouldn't automatically assume that it provides an edge.