" employing people that know stuff is simply not in their interest"
Does the stuff these people know have to be true?
I see many uses for FOSS in big business. I don't see a lot of FOSS accounting systems out there making noise. The two with which I am slightly acquainted are Deltek's CostPoint (which gives you a choice of Oracle or SQL Server on the back end) and Microsoft's Dynamics (which lets you choose SQL Server).
An FOSS accounting system would I suppose continue to work under the conditions for which it was developed. Tax laws and accounting regulations change. Are the FOSSers going to find the creation of tax updates as engaging as the development of Drupal modules or yet another CMS?