No doubt its explained fully in the topic Richards Linked too, but its for future compatability with HTML standards. All tags should have a closing tag there for those that have traditionally never been closed such as <BR> and <IMG> should instead have the backslash at the end ie <BR/> <IMG src="..."/> I haven't checked the source code but I don't think in Snitz it's yet been applied to <IMG>
I would like to work on a fully WAP version of snitz. It would be in XML, but with a lot less graphics, images, and no administration options. (it'll be made for WAP-enabled cellphones)