Lucas seems to be saying Sith lords are really nothing more than cowards who when cornered and unarmed will beg like a scared child for their life, waiting for an opportunity to strike out.
The alternative theory is that Palpatine, being the master manipulator, knew Anakin would be on his way and it was all an act for show. He certainly let himself get beaten and didn't use force lightning until Anakin arrived. His fight with Yoda showed how good he is, which tends to negate how he lost to Windu to begin with.
I subscribe to the latter theory.
Ian is a great actor, and that was such a nicely filmed sequence.