While they all market Iceland as being to Reykjavik, all of the flight use Keflavik airport a 50 minute coach journey away. A really superb little airport, it has to be said. And while Reykjavik does have an airport, which can handle up to 757, it is just for short and domestic flights, Dash8's and F50 a plenty.
In Keflavik, the airport operation in impressive, Icelandair time their US and European flights to coincide in each direction to enable connections between both continents, hence for e.g. Around 4-5 pm a big way of 757's are all leaving simultaneously and the airport is buzzing ...