The old debate continues, what is marketing and what is PR? Is PR not just a part of Mc Carthy's Marketing Mix? Check out Cutlip, Center and Broom for a full debate on this, however I would tell you that if you take pigs to market you would get some money for them, however if you don't take the pigs but get every one in the market to talk about how great your pigs are you create goodwill for the pigs and by extension a loyal demand.
The end result of any good marketing strategy is increase sales, the end result of a good pr strategy is a favourable environment for the company to operate which by an invisible thread (to those who chose not to see the connection) also translate into sales.
Now the new buzz is event planning and everyone and their mother is an event planner/pr person. Someone asked me about this recently and the simple explanation is that an event is the end product of a PR strategy. So no, you would not see me coordinating a wedding, but a trade show, press conference and the like of course.
Sometimes PR persons may choose to hire event planners or they may do the event themselves as this is a skill that most practitioners develop because of the nature of the job.