The people that are complaining about pollution rather than global warming might be thinking about the particles that aren't pleasant and/or healthy to breath in. Global warming is a problem for everyone (though the effects of it may vary depending on where you are on the planet), while pollution is for some a more local problem. If, for example, all cars in a city were converted to electric cars there might be more net pollution (maybe - could be all hydroelectric for example), but the pollution itself would be concentrated around the power plants, not in the city itself. So then you won't have to deal with pollution if you live close to one of the main arteries of that city.
There would still be less net pollution in your example though as the total pollution from using petrol to power the cars would still exceed the amount of pollution from an oil burning power station producing electricity to power the cars.
