In the meantime, following muru's suggestion I created a userscript which underlines almost all the links on askubuntu.com:
// ==UserScript==
// @name New Userscript
// @namespace http://tampermonkey.net/
// @version 0.1
// @description try to take over the world!
// @author You
// @match http://askubuntu.com/*
// @grant none
// @require http://code.jquery.com/jquery-latest.js
// ==/UserScript==
/* jshint -W097 */
'use strict';
$("<style type='text/css'>a { text-decoration: underline; }</style>").appendTo("head");
It's not the best thing in the world. It requires JQuery and overrides existing CSS rules by adding a custom <style> block at the end of the <head> block.
However the result is pretty good.
To install it simply install Greasemonkey (Firefox or derivatives) or Tampermonkey (Chrome / Chromium), add the script and enable it.