When building 1/2 A size planes, electric power really starts making a lot of sense, not just for practicallity but also from a pure performance viewpoint. You replace the throttle servo, fuel tank, and reciever battery with a ESC/BEC combo and a li-po battery. A TP 900 mAh 3-s lipo weighs about the same as a 250 mAh 4.8 volt nicad reciever battery BTW. (about 60 grams) With lipos and brushless motors, you can actually build a lighter and more powerful RC plane than is possible with glow in this size range, not to mention that it always starts. Electric power has breathed new life into small model airplanes.
You have to be a real glow fanatic to power these planes with glow engines, but then again, this is a hobby so do what you want. There will always be people that use 1/2a engines for the same reason that some model railroad buffs use actual steam powered locomotives.