Simply not spending $$$ on a third party app doesn't mean that they are saving out this money. Dealing with pst-files is a costly business as well. To name a few;
-they take up more space and thus more backup and restore time and increases the $/MB ratio
-the restoring and troubleshooting process is much more labour intensive and most often requires support from your service desk. Dropping pst support will reduce the amount of calls and put the admin back in control
-the user doesn't always have access to his/her pst-file (like by using OWA or RPC over HTTP) and might not have access to information required to make certain decisions and therefore delaying business processes
-do you really want the users to spend x amount of time a week on archiving?
All those costs together can add up to a lot making a 3rd party app or even an additional Exchange server not that expensive after all.