The domain name provider I use[1] takes $2 less per year for a .com compared to a .info.
Additionally, as a web developer, when I see squatting on a domain I want, I will be absolutely livid. Give me a place to report squatters and I'll happily help you crowd-source what was previously a Hard Problem.
It could even be done through the registrars: for every year you hold onto a domain, the registrar withholds another 10% if/when you sell it. Legitimate companies and people wouldn't suffer, since they would want to keep their domains more or less forever. Those looking to flip domains would have to consider their diminishing returns.