I failed English in High School and at the time I thought there was little use for it in the real world. But, I have found since that an ability to form a proper sentence is becoming more and more important. Maybe I'm just becoming more traditional but I even go back and edit my posts if I find an error. So yes, I think the rules should apply.
I wrote my GMAT about 6 years ago and did very well on the written component. In graduate school, I always got top marks for anything written because I truly don't believe that most people can write anymore. If you can string together two sentences, you'll do better than 90% of the people out there.
These things bother me:
You guys's (as in "I want you guys's opinion...)
Texting shortforms used in written work
And I will go to my grave defending the double space behind a period.