How is it not full-screen"? It is so much full-screen that you are complaining that it should be less-than-full... like in Windows.
Skip down to the last paragraph to see how to get the "like in Windows" effect. Read all of this to understand why the other apps (Finder at top, Dock at bottom) are gone when you choose Safari to be 100% full-screen.
Windows users who switched to Mac OS complained for years that Mac OS browsers do not have a little button at the top bar of the window to make the window jump open to fill most of the screen (I say "most" because it NEVER fills over the task bar in Windows-- it is "almost-full-screen"). They completely ignored the fact that Mac OS has ALWAYS had a simple method for this: Resize the browser window. It changes the preference file so the browser will always remember this "almost-full-screen" placement.
With Safari version 6, Apple added the option not only to have the same as Windows, but to add a little button for those who love little buttons. It wouldn't make any sense for this button to do nothing new and simply activate the resize effect that has always been in Mac OS, so Apple decided to make it EVEN BETTER. They trumped Microsoft by making it really, truly full-screen, and no "task bar" (Dock) showing.
I can imagine the discussion among the Apple engineering staff...
"Windows switchers are complaining that Mac browsers don't have a full-screen button at the top bar."
"Huh? They can resize and done, full-screen."
"No, that's not enough for them. They love that little button."
"Well, what can be gained by giving them a button if they already can do it just by resizing?"
"Beats me. They just want it."
"That would be bloated code making the browser larger than really needed, like most Microsoft apps."
"Then let's find a reason for a button so they will be happy and we will not be adding pointless code."
"Hey, how about a true full-screen that auto-hides the top menu and the Dock?"
"Oh, cool! They should be double-happy for that!"
Move the cursor to the top bar, and all the way to the right you see double arrows. Click. That cancels the "really, truly full-screen" effect. Now you can resize like before and Safari will remember what size and position of window you like ("almost-full-screen").