Good quality bikes have well sealed bearings and should be fine ridden in the rain, as long as the parts don't get submerged. Use a 'wet' lube (some type of oil, not wax), and wipe down and lightly re-lube after a rainy ride.
ALso, if you have rim brakes, wipe off the rims and pads occasionally during the wet season or the road grit applied by the water will wear through your rim sidewalls until they fail. Disc brakes don't require this step.