PrimeTime vs. Design Compiler for static timing analysis

[3wais]

I'm new to static timing analysis, I have been reading Prime Time's user guide before actually using it. Most commands mentioned are shared with Design Compiler, and the user guide says that most shared commands are either identical or have slight differences.

my questions are why do I have to save the design in DC and read it again in PT to run the exact same commands? why not use the same reporting and analysis features in DC instead of PT? and why would anyone pay for a license for PT when he can use DC?
actually the most important question of all is: am I using Prime Time right? what I was reading was "Prime Time : Fundamentals User Guide" should I skip this and go for other advanced user guides?

 

[rca]

Design compiler is a synthesis tool, with could report timing (and more...).
PrimeTime is at least STA tool.

 

[jbeniston]

The PT timing engine is more accurate than DC, so you can't rely on DC. The path coverage isn't also as high in DC.

Why PT isn't available inside ICC is a puzzle.