I sort of disagree, and here's why:
In your assessment of the situation, the equation is:
value brought to company without overtime + value brought to company by doing overtime = salary
but the overtime is paid, so: value brought to company without overtime + value brought to company by working overtime = salary + overtime pay
presumably, what's negotiated annually is salary. if overtime is compensated separately, then it really should not figure into salary discussions outside of maybe some small consideration for their not having to staff a separate on-call team.