Sounds great in theory, but in reality 'the giveaway' is only 'an install of the software within a 24 hour period'. The way most of the developers who offer their software doesn't include the ability to install at some stage in the future.
This discussion has come up several times in the past and the official line is the giveaway can only be installed and activated during the 24 hours while it is "featured". If the giveaway developers wanted everyone to be able to install that version at any point in the future they could release the software as freeware.
Of course at such a time in the future when a user finds it necessary to reinstall the software - or desires to upgrade to a newer version, naturally the developer of the software would hope that the user would consider registering the program.
So the "conditions" on the giveaway restricting against future version upgrades or "re-installing" software for an indefinite period into the future, are clearly to protect the developers commercial interests in the software to ensure the potential for future software sales.
The "right" that some people they feel they are entitled to - being able to reinstall the software whenever the need arises - is something not provided under the terms and conditions of the GiveawayOfTheDay daily downloads. To have the rights and conditions normally associated with most licensed and purchased software (such as support, future upgrades, and the ability to reinstall the software in the future -after the 24hour giveaway period) the software should be registered with the developer.
And to increase sales and get new customers is the reason why software developers "giveaway" their programs. It's promotions. Marketing. It is also a great deal for users - but if "free" users weren't restricted to a 24hour install window - obviously the software would end being treated as a type of "freeware" (probably ending up on freeware software library style sites)
If the software is good enough - users will need either a carrot or a stick to motivate them to decide to register. Some users don't need much motivation - the desire for new features or bug fixes is the carrot that results in a sale. For other users, the thought of doing without their "favorite program" - the inability to install after a rebuild and the desire to keep what they have - could be viewed as the stick that results in a sale.
If the user doesn't feel the software is good enough - they will either uninstall straight away - or just leave it installed - and should it stop working or be lost through a system rebuild etc, the user just forgets about it.
But, (not directed at any individual) ask yourself... if something happens, and you lose your free software - do you want or need the software back enough to warrant purchasing a full license for maybe $30 or whatever - and getting all the benefits and future upgrades etc, or is the software such that you can just shrug your shoulders and say... "oh well, I'll just find something else to take it's place".
Finally, most software "types" are also available in the form of freeware - sometimes rivaling the commercial alternatives. Hopefully it works out that competition between the free and commercial software offerings will result in the quality improvement in both (My experience and observations often appear that freeware and open source software continues to "raise the bar" on commercial software).