It goes way back to the old days. The old Streamliner (a.k.a. Heritage) coaches did not have center armrests. As Steve points out, this made it very easy to stretch out across seats for overnight trips, assuming the adjacent seat is vacant (which is often the case).Superliner I coaches originally did have center armrests when they were first introduced. As someone who was accustomed to the older cars without the armrest, I hated having it there for reasons just described. 
It did make sleeping a good deal more difficult.
I don't know when they were taken out, but at some point they were, and I am grateful. 
However, some Superliner I cars which still have the original seats still have the "evil plastic divider" (EPD) to which the armrest was mounted. If you look closely at the EPD it has two metal caps where the armrest was originally attached.
Superliner IIs and refurbished Superliner I cars have cushions that meet without the EPD, just a slight crack in which to lose coins. 
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Trust God, love your neighbor, and never mistake opinion for truth.
-Mr. Toy
The Del Monte Club Car
[This message has been edited by Mr. Toy (edited 04-02-2002).]
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