Have newspapers and magazines changed much from the 18th-Century to now? I do not think so. At least, not very much as far as content goes, but there is no question that the formatting and style of them has changed significantly.
One needs only to look at the difference between say, Spectator and The New York Times to see some obvious differences, with the most obvious being the difference in amount of images present. Now that technology has improved significantly, with inventions like the computer and the laser printer, it is much easier for a newspaper company to include images in their paper. Before, each image had to be hand carved into a piece of wood and the image was stamped upon the paper. Of course, now it only takes moments to download an image and format it into a paper and print it.
As far as content goes, I do not think that much has changed. People still want to know about what is happening around them, and will seek out newspapers or magazines like National Geographic or Time, or they wish to know about various celebrities or anything like that and will seek out magazines like Cosmopolitan or any of the other hundreds like it. This will always be true, I think. Only the language and syntax that is considered correct will change.
As far as my writing goes when in a private sphere versus when I write on something like this blog, I definitely notice a difference. When I am trying to write for an academic paper or something more scholarly, I will try to use a voice that matches that appropriately. I am not trying to show conversational flares or make people laugh or smile. I am seeking to inform, discuss, or argue. I am also seeking to prove that I can write on an academic level and do not write substandard for my college level.
When I am writing for something like this blog or on Facebook or whatever, I am definitely a lot more casual. Just being able to use first person pronouns opens me up to being a lot more jovial and less scholarly in my jargon and the way I present ideas. I like to make my writing for public things a lot more easy to understand and enjoyable to read overall (whether or not I succeed in doing so). I do not want people to think I am overly pretentious by using words that someone who is not an English student or does not read much would know. I think that is pretty apparent even through this post. Either way, I think there are appropriate times for both, but you have to know when to switch between them.