I used to do that. Then I got a new job that requires Windows 7 and emacs can't start in daemon mode. :(

Gnuserv + Gnuclientw

But I have not yet found a way to make Emacs close all frames and keep server running.

But it is better than restarting Emacs for each file...

always demand a linux work station! :-)

why is that not the default behavior then?

The default behaviour is a bare emacs which starts damn near instantly. If you start adding stuff then it takes time to load, but at this point you should know the daemon is an option.

Because it would take up memory from everyone, including non-emacs users.

I think that the best default approach would be to start as a normal emacs process but revert to emacsclient behaviour (i.e. just open a new frame) if a running instance of emacs is detected. This is what web browsers do, for example.

Luckily, all that takes is:

   alias emacs="emacsclient -a '' -c"

But you're right, I wish that were the default.