Upgrading for free Apple trialware from third party distributors?
As MacTrast discovered, it's not a bug, Apple is intentionally upgrading older Aperture, iWork and iLife versions (paid, trial, pirated or otherwise). 


  [However,] it’s no coincidence that Apple’s support site doesn’t have downloads for the new Aperture, iWork, and iLife updates. They aren’t in our Software Update system either – and there’s a good reason for that. With Mavericks, we have changed the way we distribute updates for legacy versions of our apps


So "legally", downloading the trials from another site just to get the free upgrade is still pirating software you're not entitled to. Apple is just taking the stance that:


  We like to believe that our users are honest, even if that belief is in vain.


Also, the Aperture trail page does specifically state that you need to uninstall the trial before purchasing it from the Mac App Store.