ORIGINAL: Fastsky
2 strokes also have a much shorter break in period which means you can get flying sooner. 2 strokes are considered flyable after 3 or 4 tanks of fuel have been burned. With 4 strokes I have read where some consider that you are supposed to burn a gallon of fuel through a 4 stroke engine before you even mount it on the plane! Thats a lot of fuel and running time with out air time. Nuff said![8D]
The instructions on the most recent 4 stroke I put in service, an OS FS-30, said to run one or two tanks on the ground and then start flying. Obviously they also contained text about running it appropriately rich, but the point is the manufacturer specifically said to go ahead and fly. I think the gallon recommendation comes from people who a) are extremely cautious, b) need very high reliability imediately due to some special application such as racing or aerobatic competition, and/or c) have too much time (and money) on their hands.
For the average sport flier, those just boring holes in the sky, most engines can be put in service after just one or two tankfulls on the ground.