Whenever seated at an overwing emergency exit on a short/medium haul flight, I have always been briefed by cabin crews on western airlines/major carriers about that fact. Long-haul flights do seem to be different though, and I do not recall the last time I was briefed at an emergency exit seat crossing the atlantic, I think Air France did last time though?
As a frequent flyer I have noticed an increasing trend in the last 2-3 years or so of unsuitable passengers (elderly/huge/children) being seated at Emergency Exit seats with no action taken by cabin crew to intervene - and I belive this is solely due to the selling of these seats at a premium by certain airlines, even some legacy carriers do it now
. I think that the "business" of selling off these seats at a premium is a safety issue and should be stopped by the aviation regulators worldwide. Any airline that does this is not interested in your safety onboard the flight, money is more important to them...
Regards SD.