Suzi, the link you mentioned in your first post states the issue of roots with clay pipes. My house is 30+ years old, has a slab foundation and the pipes from the house I think are cast iron or some kind of metal - point is they are not PVC. The reason I mention this is because over the years we have had some sporadic plumbing issues with one of the bathrooms, specifically the commode. We rented for a long time and the landlord just didn't take care of it effectively. We bought the house and a few months later we had issues again! I picked up a toilet auger and pulled out a small piece of root!!! Our bathrooms are located in the middle of the house and about 15' to the closest wall. The plumber came and pulled out a mass of roots like a horses tail - the pipe was packed, no wonder we had issues! God knows how long they had been growing in there.
I am not a plumber, but my understanding of this is when the pipes are metal the seams end up with small hairline cracks over the years due to settlement and ground movements. The roots find their way into the cracks and start growing in the pipes.
I don't know which tree or shrub the roots are from, there are several candidates since we do have foundation plant beds that have been there for over 20 years (that's how long we have been in the house). We have crepe myrtles, hollies, red tipped photinia (gone since last year) gum bumelia ( fairly tall slow growing tree) and there is a white ash about 20' from the house and we had a poplar about 15' from the house.
If you are concerned about some sort of damage, you may consider having a plumber come out and scope the lines to see if there are any cracks - that may help you make a better decision.