Boing Boing is wrong. In this story, the headline is, "AOL: Screw you, we're taxing email anyway."
Now, I know that what America Online is doing sounds like a tax, but it's not a tax because America Online is a private company. Unlike true taxes, which are imposed by governments and backed by the [if necessary, deadly] use of force, America Online's so-called "tax" is nothing more than a business decision.
I could see calling it a "tax" for practical reasons, even if it technically wasn't, if America Online had monopoly control over email. However, thisn is defiitely not the case. Google, Yahoo, Microsoft, universities, ISPs, etc. all offer free email that is as good if not better than America Online's. Moreover, one could take their destiny into their own hands and get setup their own email service by starting their own website (for which the options are literally infinite). If America Online thinks this is a good business decision and it turns out not to be, they'll suffer the consequences and lose customers to their myriad competitors.
America Online cannot [legally] use force to make people comply with this new program. Therefore, this is not a tax. This guy agrees.