It's just a form of interpreting the Quraan. Different folks are allowed to interpret it differently, not just blindly follow a cleric. The observation is good; why do some people have a problem with good observation?

Don't bring up the two calenders here because the Islamic calender is no where mentioned in the Quraan. It was created by the Sahabiah(companions of the Prophet PBUH) after the Prophet's (PBUH) death, just so that even moslems can have a calender of their own. Before the calender, folks used to follow the moon cycles.

The beauty of the Quraan lies in the fact that our Prophet wasn't a very literate man. The beauty of the language is simply astounding, and the facts vast. If you want scientific evidence on the accuracy and the truth of the Quraan, then consider this: It has verses which elaborately elucidates foetal development in various stages. Foetal development has been studied for centuries and only recently did scientists figure out the different stages. Muhammad(PBUH) was an illiterate man, he couldn't have written so precisely on something even intellectuals of then had no knowledge. Plus, the Quran has never been edited.

If you don't beleive me, check out the translation of Quraan,22:12-14