I'm also skeptical, but I think the comparison with regular dev salaries overestimates the money that would be needed, at least for some projects. There are many volunteer contributors to open-source projects who would be willing to move to working on them full-time, or at least more-time, for much less than market rate. For example one of the SBCL devs did a lot of work on the compiler for only $16k (http://www.indiegogo.com/projects/sbcl-threading-2011), and the Git-Annex Assistant guy worked on it for a whole year for $25k (http://www.kickstarter.com/projects/joeyh/git-annex-assistan...).

Granted, if you have to hire devs not already part of your project at market rate, things will go way up from that.