This pricing isn't really accurate, as you can also sign up for Unity's subscription service, which now has no set time limit on how long you have to sign up for. So, you could create your entire project in Unity, for free, and only sign up for the subscription to push it out to platforms outside of OSX/Windows/Linux. I've easily saved thousands of dollars using their subscription service instead of buying each major release outright, as was required previously.
So that means implementing Pro's features last-minute then, huh? Because Pro has some really nice stuff packed in that Free lacks. I guess it's not a big deal if you already know what you're dealing with but of the Indie devs I know, they'd rather outright save up for Pro and not have to worry about the rest.