You're right, it may work and do the job, but with Paid you usually get quicker support and better features (sometimes)
Example, FlashFXP pwns FileZilla in terms of ease of use, connection stability, and features when trying to access your FTP server
Another example, Ashampoo Burning Studio 11 beats everything i've seen when it comes to GUI and ease of burning any CD/DVD/BlueRay disc you want
Another Example, nothing compares to Kaspersky Internet Security or Eset Smart Security when it comes to Antivirus suites, yes MSE and Avira are there, but they have some false positives, do not update as frequently as the paid ones do, Comodo Internet Security FREE is a good alternative but it is a resource hog, trying running a scan, your computer would be useless in terms of speed hit you get