No, incase you did not notice, most people here dont care too much about grammer. Some might, but most people don't worry about it much in a informal shoot the **** forum. But I see what you are saying, I think.
I think my reaction to incorrect contraction usage (and obviously improper grammar in general) largely depends on context. Pretty much any simple grammatical errors in a business communication leave a very bad impression of the offending business. At worst it shows ignorance, and at best it shows inattention to detail. Are those possible attributes you're looking for when looking to potentially use a company's services?
Now, people do make mistakes from time to time. But if it's something that's recurring throughout a website/document it gets to be extremely irritating to people who know some basic grammar (again, speaking in terms of 'official' communication from a business).
In terms of less formal communication such as forums and instant messaging (and to a lesser extent email) it's not such a huge deal. People make mistakes when typing things in a hurry. Some people might simply not know that they're making a grammatical error (maybe English isn't his/her first language?). Others simply don't care in such an informal setting and will purposely not use apostrophes because it'll save them a keystroke (the laziness excuse).
In the end though written communication is a pretty powerful thing, and any obvious incorrect usage usually leaves a rather negative impression (whether justified or not) so it's in a company's best interest to make sure that everything is correct.