to me this seems an odd way to get people to purchase a license, I wonder if it actually works to any great extent..
In fact there was one case where Microsoft used open source to destroy an entire software niche on Amiga: they acquihired the developer of Bars & Pipes Professional and got him to open source it, destroying the market for Amiga sequencing software. When you consider that musicians have kept their old Atari STs going until well into the 2000s, that market was bigger than you might have supposed.