It occurred to me the difference between tag and taglink, as described in http://ikiwiki.info/ikiwiki/directive/tag/ is just that the latter enable the option to have a displayed form of the tag different from the tag itself, e.g. a tag foo can be displayed as bar using

[[!taglink  foo|bar]]

while with tag you can only display the tag foo as itself

[[!tag  foo]]

Is that it?