Is the EM5’s Miss-Stated ISO concerning to you?

was more a response to the perception you were accusing Olympus of fraud rather than simply stating you really need a given ISO/F stop to result in a given exposure time, regardless of camera.  One way to check how well the camera will work for your purposes would be to check a photo site like Flikr, see who's using the E-M5 for astrophotography and ask them if the discrepancy is an issue...

--
Art P
"I am a creature of contrast,
of light and shadow.
I live where the two play together,
I thrive on the conflict"