OB,
good question. I'm guilty of passing along heresay. I didn't really research it when I first decided not to use solvents on my doubles. Some others here years ago mentioned an issue with weakening the solder joints with "lead solvents". I am not sure if there are indeed solvents that actually work on lead, but they certainly advertise them as lead removers. Also, would a "copper solvent" act on the tin/lead alloy?