I'm not sure why, but the "there is no open source business model" discussion has woken up again, with Matthew Aslett and Stephen Walli in particular chipping in views. Last time this debate arose was when 451 published a report of the same name. That report made quite a few people in the FOSS communities unhappy because it propagated the "open core" view that a business with an open source element somewhere in its activities (what Stephe calls a tool) could be described as an "open source business".
Why is there no "open source business model"? Because open source is not a business. It's the same oxymoronic thinking as the question "how can you make money if you give the software away for free", which simply can't be answered without correcting the questioner's worldview.
To assert there is "an open source business model" is to lose sight of the nature of open source. It may have been a fair thing to do when open source was a novelty to business minds, but even considering there could be such a thing leads people to misunderstand open source and treat the exceptions - like MySQL - as the rule. Not that it's wrong to monetise ubiquity at the point of deployment by delivering the value that allows scaling (enabling adoption-led behaviour). It's just most open source community members don't do that.
An open source project is a community of participants that gathers around a free software commons, with each participant aligning an element of their interests with the interests of all the others there, in order to collaborate. The OSI-approved license gives them the freedom to do so. Each participant comes to the community with their own individual interest, which in the case of a business will stem from their own business model. The community itself is about the Free code in the commons. Just about the code - all other matters are subjugated (at least in working communities!).
An open source community is thus a mix of many motivations. If there's only one motivation present - only one "business model" - it's unlikely there is any true community either. People only care about the business model when there's only one business; in a real community the only way to get along is to mind your own business (model) and not try to mess with anyone else's.