Does windows have an image of security?

I am just wondering because today a girl in one of my classes brought in her Sony Viao Laptop and set it in a room and left. Before she did i asked her if i could see it she said yeah but i have a password so you wont get very far. (Side note you should not tell people that they will not get into your computer if they have anything to do with computers) Well i opened it up and turn it on and started guessing words that i though she might use as her password and after about 3 minutes of not getting anywhere i decided that I should take a different approach. So I turned off the computer and then turned it back on and as it was first booting I set it to start in safe mode. I purposely eliminated posting what buttons i hit becuase i dont know if it would be appropriate. Once safe mode loaded (this is one of windows major flaws) i chose to login as administrator ,which has no password enabled. Then i opened the control panel and selected user accounts and selected her account (another one of windows major flaws) which gave me the nice option of removing other user's passwords. So i removed her password and then restarted the computer and logged in on her account.

Well i saw her a few periods later and she was utterly suprised at how i had "hacked" into her laptop. I told he that it was very easy. Then she accused me of using some software program and i told her all i used was windows. So i had her put a password on and then while she was looking at the back of the laptop to make sure i had no cd to put in i once again removed her password. She was very upset and could not believe how quickly i had done it.

So basically i was just wondering if alot of people think that thier password on windows is a safe way to keep people out. I personally do not have a password becuase i know how futile it is to try and keep out someone who has any know how of computers. I instead just encrypt the files that i do not want people to view.

Also is there some way to add a password to the windows administrator account? A registry hack maybe? or even a way to remove the option to remove user's passwords?