Yes. Four reasons.
First, demographic. The Internet used to be all nerds, and the kind of nerds who lived and died by their ability to write well--fellows like Linus Torvalds and Bill Gates and Steve Jobs. They carried their formality with them like a knapsack. Now, everyone's on board, and not all of them are paid to speak or write clearly.
Second, informality. The Internet used to be that sort of place, and then it was big-business buying and selling in addition to research. Social networking used to be segregated pretty severely from this stuff, and the styles were pretty different. Now, we seamlessly copy from Facebook to Wikipedia to TVtropes.org to, well, here, and the laziest rules and styles spill over.
Third, fatigue. The first time I laid out a reasoned, well thought-out disproving argument against "Ladder Theory", or a calm, scientific dissection of why "going postal", school shootings, fight clubs, and bullies are linked, I was proud to do so. Repeating myself now--for the umpteenth time--seems like a waste of effort because I can assume everybody's read it (as if!), read something similar, or dismissed my ideas already. In larger terms, the big arguments have all suffered this kind of thing--obdurate people know the arguments and won't be swayed, the champions of the ideas are tired of shouting at the walls, and the Internet doesn't lend itself to wall-of-text reading. To prove it, I'll throw in a random quote to prove to myself that you didn't read this far: purple monkey dishwasher gober my daisy heads. The final point has your attention already, doesn't it?
Fourth, a sense that the Internet is "other" than real life. Simply, we turn off the business brain when we're on here, and the rules relax. Related to the general informality of the Internet, but specifically for all those live-and-die-by-writing people.
Fifth, anonymity makes f___wads of people. You knew that already--around here, we don't hide prejudices, we use them to stop debate and start arguments.
