Best I can tell (law not being my vocation) the IRS formalized things such that not only are winnings taxed as capital gains, but losses are also a factor.

This is key because it allows people with real money to put some of it on the table and enjoy at least some tax advantage if Bitcoin experiences some sort of a failure or collapse.  I would expect more speculation from those with deep pockets for that reason.

This isn't the only reason why the formal guidance from the IRS as it came down delights me, but it is one of them.