> It doesnt have to be complicated at all

Indeed.
The example you gave was electrically identical to my second one.

> you dont HAVE to have two windings in parallel as long as one of the 
> windings can handle the additional current at 110 volt

Indeed. But in any "serious" application attempts are made to optimise 
the winding windows used by primatries and secondaries. By not using 
one winding at 110v you are using the resource less effcieintly. In 
many cases this will be an acceptable tradeoff with simplicity.


        RM

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