I don't know either but it would have been cool to of had two pipes and mufflers for looks,but that would have cost money.

A lot of jap singles, especially dirt bikes, do this.  Same with European dirt bikes like KTMs (now they're a nice dirt bike, but very pricey).

They tend to run a 4-valve cylinder head and out through two headers then a collector about 18 inches later, or some are siamesed into a single just an inch or two out of the head.

Those were the bikes that my MSP class used... I thought it looked a little funny too.

These are a couple of examples of twin header exhausts for single cylinder dirt bikes.

One with clearly separate headers:



One with a 'siamesed' header

toddlamp8 wrote on 06/25/08 at 14:48:53:
On a 4-valve head the job of bringing the ports together has to be done in a longer exhaust tract, so that would probably cost a little weight in extra cylinder head material.

As for cost, it's always a matter of balancing cost against efficiency/power, and the costlier designs are there to give you better performance.

Life's a compromise I guess.

Yes and two spark plugs as well. (I used to own one in the late 80s)

I don't know why there are two either.  Like a genius, I grabbed onto them on Kay's bike to see if one was a dummy for looks.  Turns out I was the dummy.  They were both hotter than he!l.  I don't recommend this as an exploratory method on a motorcycle.