What is the difference between a Mac mini and a Mac mini server?

Apple sells two Mac minis; one is a server edition, the other is a standard Mac mini. What are the differences between the Mac mini and the Mac mini server? I know that the server doesn't have an optical drive and runs a server edition of OS X. Besides this, what are the other differences? What is the advantage of buying a Mac mini over buying a Mac mini server? (besides, of course, that the server runs OS X Server, and one is faster than the other) Will the server last longer, be able to handle running 24/7, whereas the standard one won't?