You must be kidding? I've found the exact opposite to be true, 99% of the time.
Spelling mistakes and grammatical errors will be a product of a persons education and environment regardless of the era they grew up in, but those of us baby-bloomers and Gen X'ers who were raised "pre-internet" were taught to use proper grammar and punctuation and did/do so on a regular basis. Some didn't do it well, but at least there was an effort made.
The excessive use of acronyms, lack of punctuation, plethora of basic spelling errors and downright horrible use of the English language you see littered throughout the internet, now a days definitely a product of the "nobody comes in second place, everyone gets a trophy and its my duty to question everything", late-Generation Y and post Millennial crowd. The sheer laziness and sense of entitlement displayed by that generation is staggering.
They're easy to spot. They're the ones who barely remember life before cell phones, are are continuously getting defensive and calling you a "grammar nazi" when you call them out on their lackadaisical attitude and utter stupidity.