Really? I know a couple of guys who work nights at Wal-Mart, and they make around $10/hr.
http://www.glassdoor.com/Salaries/night-stocker-salary-SRCH_...
I would assume it depends on the part of the country you are in as well.
In any case, I don't believe that these companies will give overtime. In fact, your glassdoor link doesn't show any company paying over $30,000/year to their night workers, with the average being around $25,000.
Assuming the position required 60 hour work weeks(as a non trivial amount of developer positions do) this is what the two would look like for exactly the same final pay.
With salary one can say: $50,000/year
With hourly one would say: $13/hr + overtime
While being the exact same pay, it looks quite a bit different. No?