Now, some may say that even these types of models will still go against Blizzard's rules (in fact, the rule that says addons may not charge for distribution also hints that they may not charge for "services related", either), but at this point, we don't really know what these rules mean, since, as far as we know, Blizzard hasn't actually shut down any addons. Blizzard may be trying to say that any attempt to make money off of an addon will get it shut down in the game (a strong statement, since you'd think anyone putting time and work into an addon should get something back for it). And if they really do have issues with people who help players play the game making money off of it, what about sites like Wowhead? What about us here at WoW Insider?
At any rate, the ideas are out there. If developers really want to get something back for their work, and they have an addon or an idea that's worth paying for (keep in mind that competition is always there -- if an addon like Recount does charge to go visit another site and get DPS meters, they'll have to make sure it's worth paying that amount rather than just using a free addon), there will probably be a way for them to get compensated.