Star System Attack

Just a question to gamers/astophiles (I think thats the term ! And I
don't
mean the green stuff!!)
When in Sci-fi (or FT) you jump into a system , it always appears that
you
are beyond the outermost planet. Hence the 'defenders' have time to
muster a
defence and come out to meet you (Cut the last jump close as the KV did
in a
MT senario and you shorten the muster).
What I want to know is why is it always on the solar plane? I would have
thought that jumping in over the poles of star would mean you could be
'in
system'. The solar wind (Correct me please) is concentrated along the
plane
so polar jumps would be safer (same with debris)? What gravitationally
would
the difference be ? (fast spiral as opposed to a drag orbit?)
On a gravity space-time distortion map I would have assumed no
distinction
between planear and polar 
Jon(T.C.) How the hell are we assuming H-space works anyway RE FT II ?
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