I agree that (sometimes) the conductor of an orchestra can appear to be superflous;but a GOOD conductor shouldn't be!
Up till the middle of the 17thC there was no such thing as a conductor.
The orchestra would (usually) be kept in time by the actual composer of the music that the orchestra was playing.
Wikipedia has a good article (that says more that I can) avout the history and role of the conductor.
http://en.wikipedia.org/wiki/Conducting
Personally,I think most conductors work out how a piece should sound in rehearsal.This might lead you to imagine they are not doing much when the piece is played in front of an audience.
What they are really doing is providing visual cues for the orchestra to remind them of what was agreed in rehearsal.
That is why some conductors don't appear to be conducting with a beat,they don't really have to,it's all been settled before.
It was mainly conductors before the 1960's that had set regualr beats.The more modern ones just uses gestures that the players will recognise.
The leader USED top be a susbsitute conductor,but now he is (usually) just a liason between the podium and the players.In the time of Johann Strauss (especially) the lead violin WAS the conductor,so he performed two jobs.
Nowadays,he is also the orchestra's (sort of) unofficial shop steward,and is also the boss of the orchestra when the conductor is not around,or the orchestra is on tour
PS:~
Do read the story (in Wikipedia) of the composer/conductor Lully,it's sad and yet funny!
All the above information is courtesy of my Grandson in Law,who was Leader of the Royal Opera House Covent Garden Orchestra.He is now a solo violinist.