Why are these traces shaped in such way?
What are those parallel soldered-traces on the PCB traces?
  


They are traces where some of the soldermask has been removed in order to allow solder to build up to improve the current capacity of the trace.

The reason they left the narrow parallel lines of soldermask is so that the solder distributes itself more evenly across the width of the trace. Otherwise, it might bunch up on one side or the other. The rings around the component leads serve the same purpose &mdash; they prevent solder from wicking away from the joint.

The benefit of this is actually less than most people seem to think. The resistivity of solder is about 9&times; that of copper, so in order to halve the resistance (double the current capacity) of a trace, the solder needs to be 9&times; as thick as the copper underneath. For 1-oz. copper (35 &micro;m), the solder would have to be uniformly built up to 0.3 mm or more.


  
  Why aren't they soldered to the soldered legs of the components?
  


They are in fact soldered to the legs. There is a circle of soldermask around each leg, but the copper still makes the connection underneath.