There are several options for posters to generate their links as links that will open the software centre. The basis behind all of them is linking to http://apt.ubuntu.com/p/<package-name>.
There have been discussions about making this automatic (eg to detect apt-get install ...) but my attempt to do this failed. The major problem is you'll also see add-apt-repository scattered around the site and this can be a major part to getting some things working. Adding apt repos is not possible via a link (for good reason!).