(Link here: http://community.livejournal.com/bleachness/147422.html so that everyone is on the same page)
However towards the end of the post I make a somewhat off-hand comment that I believe that the same reasoning applied to Ulquiorra. My predictions of someone swooping in and kill-stealing or a team-up turned out to be wrong but guess what... I was RIGHT!!!
It's true there was a fight between Ulquiorra and Ichigo but what happened (at least by my reasoning) is that once The Beast emerged the roles of antagonist and protagonist inverted themselves. Ulquiorra up until the end was not a fitting opponent for Ichigo via the logic governing his previous fights. However Ichigo was a fitting opponent for Ulquiorra. In my initial post I use the metaphor of a mirror, especally concerning the differences between Ichigo and Grimmjow. I called Grimmjow Ichigo's dark mirror and if I may extend the metaphor slightly Ichigo was Ulquiorra's bright mirror, emotional and hot-headed to Ulquiorra's cold, rationalality and the like.
But Ulquiorra is tormented by Ichigo's mirroring of his personality and in doing so seeks to destroy it and by doing so accidentally takes Ichigo's place. The Beast is remorseless and relentless while Ulquiorra is in the middle of an emotional breakdown. Even their colour schemes switch, Ulquiorra becoming black in his second release while Ichigo's clothes are largely destroyed revelaing his comparatively pale flesh and bone-white mask. By acting to stop The Beast Ulquiorra metaphorically takes action against his own darker nature and redeems himself. Whether he will survive or if Redemption Equals Death will prevail is uncertain.
In short, the fight was thematically consistent but with a very importantly difference with the flipped perspective.
It's little tricks like this where Kubo-sensei adds new twists to standard story-telling themes that make me appreciate Bleach more and more. Whether it's deliberate or subconscious, Kubo-sensei is at times a frigging genius!