Can't say that I particularly like or even agree with their method. You'll probably find that they had plans to sell it right from the time of its conception. By initially offering it for free -- it attracts a larger audience, some people find a "niche" for it in their toolbox, some may even become entirely dependent on it. For most people it's a "gotcha" -- they now must simply pay for it in order to continue using it. The vendor would make a tonne more money doing this than initially trying to sell it. Mainly because most people don't fall in love with a piece of software until they've come to grips with it. Even a $30 purchase for many people is enough to make them procrastinate about;

1. Will I learn this easily enough?
2. Will I ever really use this thing?
3. Does it really work a good as they say?
4. Will it do exactly what I want it to?
5. Maybe I can find something cheaper?

When something is for free, none of those things enter our minds -- instead we just give it ago because we have nothing to lose. So all told, they'll reap in a tonne of cash from basically all dependent users. That's life ...

Feel free to disagree with my marketing theory