"How a font is sold is up to the discretion of the font creator" and "a font should not be sold on a sliding cost scale" aren't mutually exclusive -- the latter's pretty clearly asserting an opinion about reasonable pricing models and terms of use. There are a lot of things people do that they're perfectly within their rights to do that someone else might strongly believe they shouldn't, right?

Personally, I don't like the idea of selling fonts with costs governed by web page impressions, either, no matter how common it may be in the industry. I genuinely like having what I consider to be nice typefaces for my web sites, but this kind of licensing makes it incredibly impractical for me to use most commercial options.