Oh there is definitely a point Vaughan. Surface rust that just forms a thin layer of brown is no problem but there are bigger issues as this develops into a harder more tenacious rust that pits the disk and glazes up. Put simply the situation can quickly decline into a need for disc and pad replacement. If car in regular use there will likely be no problem although some cars do suffer with this problem on rear discs even with regular use. My Golf, the old girl pictured has rear drums so one or rather two less things to worry about.
Talking of cigarettes flying around cars brings back memories of the 70s/80s when we all smoked and ash/rollup butts, etc flying back into the car was a common issue. I used to really enjoy smoking but happy to have given up altogether well over 10 years ago. Got hooked on cafe creme cigars with difficult withdrawal leading to complete abstinence. Have you seen the price of a packet of cigarettes nowadays - unbelievable?