I'm just going to add to your example of what people can do with a tablet, using the iPad as my example because I don't know much about the Surface.
Now, let's say I don't have a computer or an Internet connection.
I can go to a store, buy an iPad with Wi-Fi and Mobile, and then go online and diddle with Facebook, et-cetera. I can setup an iCloud account, which is needed for the Store anyway, use it for email, and so on.
If I want to have the Internet on at home I can order an Internet connection hooked up to my house, wait for the modem to arrive, and then set it up wirelessly - plug modem in, wirelessly connect via DHCP and visit 192.168.1.1 in my Browser, set parameters, surf Internet wirelessly.
If I need to print stuff then I just have to make sure I buy a printer with AirPrint OR I could use an app like PrintCentral to print to any wireless printer, or any printer connected via Ethernet or USB to an Airport Express (unfortunately an Airport Express doesn't facilitate printing to a non-AirPrint printer on its own).
Let's say I want to do a lot of typing? I am currently writing this comment using my Logitech-branded Zagg keyboard (aluminium base and nicely responsive "large" Bluetooth keyboard that attaches snugly without clips to the iPad and protects the screen). Unfortunately you can't attach a Bluetooth mouse though, and I do sometimes get "Stylus Hand" after playing Trainz for a few hours.
If I buy the adaptor kit (I believe the Surface has a USB port already) then I can connect my camera and directly transfer photos and videos to my iPad for storage, editing, and sharing.
If you have a tablet with a keyboard then it's pretty much like having a small laptop. There are times when it's lacking, such as I can do some web design but I don't think I can run a web server for testing (haven't looked too closely) or I can write a book with any one of a myriad of writing programs but I can't do some low level editing of ePub files, but still I can make music, take and edit photos, record and edit films, do 2D/3D modelling for fun or architecture, record and publish Podcasts (audio or video), write a newsletter, create a presentation for the office, organise my finances, and then of course there's all the social apps that help people communicate and find each other (Find My Friends is nifty).
Some people may never really use their tablet's full potential, but that's okay. Most people will never use their personal computer's full potential either, not even if they have Word installed (New Page Break, what's that? I'll just \n \n \n \n \n down to the next page, and make some other poor bugger deal with it when they edit this later.)
Also if you have a personal computer and are willing to experiment you can also attach an external HDD to your iPad after jailbreaking it.