That notice is from 2014 and speaks nothing of Steemit in particular. Does it even apply to Steemit? If it applies to Steemit why wouldn't it apply to World of Warcraft, Diablo 2, and every online activity?
As far as I know, that seems to apply to miners in particular. Miners are creating money or something intended to be money. Steemit bloggers are earning virtual tokens which can be traded for some unknown amount of money which fluctuates wildly. You can't use Steem Dollars to buy coffee or for anything really so it's not like Bitcoin but seems more like Linden Dollars or WoW gold which is used on this platform but isn't like real money.
Of course I could be wrong, but unless the IRS clarifies and states that this notice applies to all digital currencies, and all platforms, including games, then I don't see that it clearly applies to Steem even if some people might want it to.