This is a largely informal place. As such, 'conversational' language and grammar is appropriate. So long as you're understood, then it really isn't a big issue. If, however, you are trying to convey a particular meaning and balls it up by poor grammar or spelling, then you really should be happy to be picked up on it. You then have the chance to realise your mistake and correct any misunderstanding you may have caused. This is just life. People who bite at the slightest bit of correction from others are just as bad as the true pedants. If you don't like being corrected, then be meticulous.
I have been known to pick people up on grammar or spelling on here. I must confess, often it is out of a desire to kick the chair out from under someone who is 'giving it the big'un' on a topic and doesn't like being questioned on anything.
Anyway, don't lose any sleep over it. It is far more important not to be part of a bullying clique or a lone-wolf tosser than to make sure every apostrophe is necessary.