My last company was exactly that. "Salary Minus". I forget the exact pay rate, but lets say it broke down to $1/hr. So I'd make $40 per week based on a 40hr work week. 60hrs that week meant I still got $40. 30hrs for the week meant I got $30. These hours were against actual projects/new work.
Additionally, I was on call 24/7. Every goddamn week. A service call during the day cut into my time on new work, so I had to "Work Harder" to make up the time I lost on the new job to offset the time spent on emergency maint.
On the upside, I did get paid a fixed $50 per service call for after hours maintenance (before taxes). $50 per call no matter how long it took. 15min fix? $50. 12hr fix? $50.
This was from 2004-2006. I started at $37,500/yr and I think when I left I was up to a whopping $39k or so.
Maybe I'm a masochist, as I switched companies and kept doing the same damn thing. The customers I had switched their contracts to my new company less than 6 months after I left the old.
Still salary, still the same on-call schedule, and I lost the after hours compensation I used to have.
But now I kinda work my own schedule, act as my own supervisor, manage my own projects, work less hours and make more money.