Re: ESU\'s and Demo Jr.
Because the standalone doesn't carry central objects, and the ESU updates against central objects. It also checks to see if it is running against a deployment server when you initiate the install.
However, it wouldn't be too difficult to "fool" your standalone into believing its a deployment server - hence allowing the install of an ESU - but it'd take some trickery to get it working well (and an already installed deployment server no doubt).