@jenius yes bro thats true. Dont forget that all these are paid softwares. If they give it for free all time then it will be a piracy issue.
So the software has to be downloaded, installed and activated during the give away period.
When you install a software it will check the give away offer at that time of installation and only if it matches then you will get full version.
This is to protect piracy. They have clearly mentioned this on their website.