I'd love all those neurosurgery keen beans to come and spend a week with me on the Neuro ICU where I currently work, and see how many are still keen after that.
I think neurosurgery sounds "better" to applicants than plastics because it has the whole "hero" aspect to it - chopping out brain tumours etc - while with plastics, although the cosmetic side is glamorous, a)most plastics work isn't actually cosmetics (and is technically WAY more impressive than a good pair of boobs!) b)most medical applicants do have a fair amount of altruism and aren't solely fuelled by money. Plenty of people have naive ideas of what specialty they'd like to do before they've really experienced any, it's just that neuro seems to be trendy at the moment.