In the middle of December, Sega released a free upgrade for Daytona Championship USA on arcades. It shipped the update as an USB drive to machine owners, and then released the full software online for free. The 3.8 GB download is hosted on Dropbox, and it apparently contains the whole game updated to the current version.
According to users on Resetera, the file can be downloaded and it's copy protection bypassed with a hex editor, making Daytona 3 essentially free to download (but not play).
Of course, it is not as simple as that. While SEGA has released the full game files for free, it did so to allow legitimate arcade customers to update their machines. Downloading the game and stripping the protection away to play on PC's is tantamount to piracy, which is a big no-no.
On the other hand, people are comparing it to playing a console game on a PC emulator, which is technically wrong unless you own the game, and then it becomes a really shady issue that gets more headache-y the more you think about it.
The big difference in this case is that if Sega really released all the game files onto the internet for free, the whole "buying" requirement gets even more complicated.
Either way, we recommend you stay away from things like this. Piracy hurts the developers and consumers alike, and it's better to reward the people making the games you love so they can keep doing that. In the off-chance you do own a huge Daytona arcade, you can find the update and patch notes here.