Does it help to only have the desktop version of a site on a smartphone and tablet?

I have read/heard people “I can’t do somethings on my mobile that I can do on a desktop”, “I can’t post a link”, or “I keep getting error message when I click on link” etc. So, eventhough there is the hardware desktop computer that we can do a lot more than the mobile (the hardware), still could it be also be true that when people use the desktop version on smartphone or tablet they can do the things they couldn’t before?

Also if you’re using a tablet or smartphone do you see the tabs (some call it link) “Mobile” and “Desktop” on any site, and if not, is it iPad or Android or both?