g1smd - 6:19 pm on Mar 20, 2013 (gmt 0)
It is [NC] that allows aNyCase.
The [OR] means "or". If you omit it, ALL of the conditions must be true - so the rule will NEVER run. There is no user-agent string that could possibly satisfy all of the conditions at once. Multiple conditions are separated by an implicit "and" unless you state otherwise.
The anchors are important where a pattern could be ambiguous. They allow you to match a shorter string while rejecting a longer string.