I believe taxing subscription revenue would be more economically efficient than almost any micropayments architecture conceivable. I also don't think it's necessarily unfair on the whole; for example, consumer accounts with download caps may be taxed differently depending on the size of the cap. It's hard for most consumers to get near their bandwidth caps without consuming large amounts of media.
And if there are other uses, e.g. remote work over VPNs, specific contracts with remote locations, etc., such traffic could be exempted from the taxable cap.
One thing I'm pretty sure of: trying to sell information (i.e. bits) along the same lines as historical tokens (DVDs, CDs etc.) is doomed to failure. Steam comes with several major drawbacks: you need to be online regularly to log in, you have to put up with a client on every machine, forced advertising, higher prices than the shrinkwrapped box (the case here in the UK), etc. It's also a single point of failure in a business sense - size or past profitability is no guarantee against overreach or future bankruptcy, and the more eggs you have in the Steam basket, the more you have to lose when (and it will eventually) it goes away.
Re pirating internet access: that's inherently different, because (most) information is a non-rivalrous good, while access to a network pipe is rivalrous.