Jon,
In unscientific tests I have conducted with various wood cleaning recipes, it has appeared to me that sodium tripolyphosphate seems to help get dirty wood cleaner than TSP mixed into my brew. Like I said, I have no scientific basis, just general observation. I've tried many combinations of various chems and have found a few that seem to work pretty well. There may well be commercially prepared versions that perform better, but as long as what I'm using is satisfactory, and material costs are lower, I'll stick with my own recipes. I do use a bit of TSP in my house wash mix, however.
Since all my recipes are for my own personal use, I don't spend too much time determining "why" something works or does not work, I just go with what works for my application. However I do look at MSDS sheets to try to ensure the chems I use are generally accepted as safe.