Ermm - There are "loads of flu viruses", or more accurately lots of different strains of the influenza virus that circulate the globe, thats true. However, a lot of work is invested in matching up the strains that are eventually used in the vaccine, commonly a trivalent vaccine, and those strains that are currently circulating the globe, and therefore the ones most likely to be seen here.
To a large degree, the effectiveness of the vaccine is dependant upon how close the match is between the predicted strains, and the actual strains we see.
In fairness, most of the time, the researchers get it pretty much right, so I think saying that there is little point in having the vaccine is a bit unfair. If are in a high risk group, or if you work in a job in which you interact with sick people especially, then it probably makes sense to have the vaccine.