I think I get what you're saying – that there aren't laws to support that income from cryptocurrency has to be paid.

But I'll merely point out that the IRS document you shared says "The Internal Revenue Service today issued a notice providing answers to frequently asked questions (FAQs) on virtual currency, such as bitcoin." (emphasis mine)

So, if I'm understanding correctly, it was not "announced simply for the purpose of taxing Bitcoins." It pretty clearly includes all cryptocurrencies.