Although I don't agree about saying
to baseball, matthew is right: if the baseball season ends in a strike (or lockout, or work stoppage...), you may well see even more people playing fantasy football, and also trying out basketball or hockey.
One more minor detail: expect fantasy football leagues to add rules detailing what happens in the event of a football strike (whether the team in the lead wins, or the entire season is scrapped, etc.). You can imagine the arguments caused by this issue in baseball leagues this year, especially those with money at stake... While there doesn't seem to be any labor trouble on the football horizon, long-running leagues would do well to be prepared.