Why? Because it's the computer overriding what the user wants to do.
Open a document in TextEdit on Lion.
Close it. Make sure that there are no other documents open in TextEdit.
Click on the Finder.
Command tab back to TextEdit.
It's gone. It's not even in the list of applications you can command tab back to.
So Linc, how long have you been using the Mac? The way these apps have always worked in the past is that YOU quit them. The OS doesn't.
Many times, I'll close the last doc, then go off and surf, then come back to the application, press command O and open a file from the open dialog.
But what's worse is that the app doesn't quit. It's still running. You can see this in the Activity Monitor. The user is just prevented from accessing the UI unless they actually go back and launch the app again. This forces the user to perform unnecessary steps for no reason.
So, why wouldn't I care if the operating system thinks it knows better than me and starts auto saving everything I type, auto quitting an app if I closed the last document and so on.
We have simple methods to do this already. They are the quit and save menu items. This new push creates conflicting user experiences (which apps auto quit and which don't, which auto save and which don't). This forces the user to think about more things before they use random app features, "is my text saved", "will the app auto quit on me if I do something", and so on.
It's not fun. It doesn't help and I want to know how to turn it off.
I use my Mac to make money. For me and for my employer. I use it because I like how it operates. I do not like how Lion operates. If Apple continues this way, I'm not going to like using the Mac. And that makes me sad.