I was under the same impression and after a quick Google search came up with the following from Caltex in the Product Data Sheet for Vortex 95:
"Caltex Vortex Premium 95 is a high-performance premium unleaded petrol specially formulated to clean your car's fuel system while you drive. It has a minimum Research Octane Number (RON) of 95 and meets the Fuel Quality Standards Act 2000.
Over time, deposits build up in critical parts of your car's fuel system, including fuel injectors and intake valves. This build-up of deposits happens slowly so you may not notice the performance of your car slowly deteriorating. A build-up of deposits results in reduced combustion efficiency which leads to a loss of power, slower acceleration, increased fuel consumption and higher exhaust emissions."
From the Shell website:
"Shell V-Power (which is 98 RON) contains powerful cleaning technology designed to prevent the build up of power robbing deposits from forming on intake valves and fuel injectors."
I don't know if these claims are genuine or snake oil, perhaps the more learned amongst us could elaborate.