Not so all the time. One of the few tube replacements I’ve done was on a horizontal top tubed Stowe/Terry. There was a strip of rust along its underside going down the full length of the tube about 3/8" wide. Rider was known for lack of maintenance and winter commuting. On a repaint and refurbishing braze ones the top tube (and chain stays, that’s another story) showed poke through holes from the rust. Andy
I recently replaced a top tube that rusted through as well. I ran out of Framesaver a few months ago (finally!) and have tried a couple others like the Fluid Film pictured above. It was messy with the nozzle that goes into the tube. It sprays out in all directions so it really flows. I suppose they are all messy to some degree.