If I understand correctly, the GtkAboutDialog url should be automagically clickable, but here I can't make it work :/. Also the website-label property is ignored. 
Checking other apps, like Epiphany or Eog, I see that they do the same I do but with the expected result. Sorry if this is just a d'oh on me, but it seems like a bug to me.

Similar problem in bug #425004.

A simple program like this will show the bug:

#include <gtk/gtk.h>

int 
main (int argc, char *argv[])
{
	gtk_init (&argc, &argv);
	
	static const char *authors[] = {
		"daniel g. siegel <dgsiegel@gmail.com>",
		"Jaap A. Haitsma <jaap@haitsma.org>",
		NULL
		};
	
	gtk_show_about_dialog (NULL,
			"program-name", "Diego about dialog",
			"logo-icon-name", "web-browser",
			"version", "0.3.3",
			"title", "Powerpuff dialog",
			"website-label", "My website",
			"website", "http://diego.aureal.com.pe/",
			NULL);
	
	gtk_main();
	
	return 0;
}