I think I can sort of see the case you're making, although I don't like the way you phrased it.
Accounting and tax software needs to be very bug-free, due to how mission-critical it is for enterprises. Commercial vendors have an incentive to make their software bug-free because otherwise their reputations are tarnished. What kind of similar incentive can we produce for open source developers of accounting and tax software?
If Red Hat or someone else were to offer a commercial support contract for some open source accounting software, Red Hat would have an obvious financial incentive to keep things working. However, support contracts only really make sense for big companies, not for small organizations like LWN.net. This would also tend to drive the developers towards implementing complex features needed by large organizations, not simple things needed by a smaller operation.
In the end, I think that we could probably create a good open-source accounting package. It would have to be extensively unit tested, and the development paradigm might have to be a little more restrained than the usual rapid-release strategy. It might also be a good idea for some organization to hold a trademark on the actual name, sort of like how Mozilla holds the trademark to Firefox.
In contrast, I have a hard time imagining open source tax software coming to pass any time soon. It's just not a very rewarding thing to develop-- it doesn't scratch anyone's itch, and the rules change every year in subtle and complex ways. Perhaps the best thing we can hope for is that there will be an open standard for storing tax data. Unfortunately, the IRS's e-file standard seems to fall far short in this regard.