Do you think he's being insincere or just a showman? My feeling is that Guy likes to exaggerate everything to make a point: in this case, it's getting really cheap to fail, so take more risks.
I totally agree that you need a business "model" - but do you really need a "plan" for a site that costs $12,000?
If he can get 260K page views, even a 0.5% clickthru @ only $0.10 an ad is $130. Not great, but if you can do it every day you've got a site that's pulling in $50K in revenue a year. Not bad, but could be something to explore.
I totally agree with you that you need to know where your business is going to go and if you want to get real funding you'd better have a business plan, but if you're running a $12K test, why not just make sure you think there's a model and then test it?
Any responsible investor, either angel or VC, will want to have some sense about that, even if revenues and profits "come later".
YC gets a lot of criticism in that regard, but to their credit, they do ask applicants how they intend to make money with their project.