A subscription provides ongoing revenue to the developer/publisher, but in the case of software, that revenue is (theoretically) being used to fund ongoing development of the product. Whether this is better for users than the traditional paid upgrade model is debatable, but there's undeniably value to the developer in a predictable revenue stream, and as long as the subscription price isn't totally out of whack compared to the old upgrade model I don't mind it. Assuming the developer is keeping up their end of the bargain, so to speak, and making regular releases of the software, then it's perfectly reasonable for you to keep paying for those releases.

But fonts are mostly a different matter. It's vanishingly rare for there to be more than tiny tweaks to a digital release of a typeface after its initial release. Unless I'm paying for someone else to host web fonts for me -- which Helvetica Now's web font license doesn't seem to entail -- this seems to be considerably more usurious. Print magazines weren't charged an annual cost for their typefaces based on their circulation; web fonts should really be no different.