No offense mate, I don't think that the government is banking on raising revenue from people buying extra life jackets as its the law to already have them on the boat. However, in real life, having them on board and not wearing them is as useless as base jumping without your parachute. From observation, most fishos don't appear to be great swimmers. Therefore, when an "unexpected accident" happens, and your find yourself in the drink 20m away from your boat and 100m from shore, you will be happy that it will keep you afloat for a while instead of a slow drowning.
Besides, with the advent of modern vests, any fishing technique, or your overall experience would not be affected.