A programmer who works 55 hours a week will produce twice as much code - but for how long? Once fatigue settles in (a few weeks in), you're back at the 40-hour productivity levels, just paying it at 55-hour rates (and organizational overhead for overtime, oooh boy!), plus burning out the developers (and organizational overhead for employee churn).
Your assumption is that 55 hour weeks are sustainable: just change this number in the spreadsheet from 40 to 55, and voila! And while we're at it, why not 80? Why not 200? Very PHB-ish, in my unhumble opinion.