I disagree. The manager is responsible for turning a profit. If he can make more profit by raising wages, he would be free to do so.
I'm sure it varies from business to business, but I can only speak to how it works in the businesses where I have been managing a team. I work in professional consulting services, so this might be different to manufacturing, etc.
I am free at any time to add additional staff, with the assumption that any staff I do add will become utilised and chargeable to our clients. If I suddenly add 10 people, the heat would be on me to keep them all busy. We are aiming to make about 30% as a base profit on each employee in the team. If I am paying them $1000 a day, then I need to sell them at $1300 as a minimum, and keep them very busy.
When I am hiring, I have a fair amount of discretion in the wage I offer. There is oversight, but it's something I can have a fair amount of control on. Yearly salary increases are a different story, because they are not built bottom up in the same way. The business unit is effectively given a global revenue budget, based on existing staff numbers, plus forecast hire numbers, and allowing for 'normal' levels of loss.
As a simple example, I might have a total staff salary pool of $2,000,000 this year, and be funding for 2 new hires, and a $100,000 increase in existing staff salaries.
In theory, I could give that whole $100,000 to a single employee, and tell the rest they are getting nothing. There is oversight of this process by my manager, and by HR to prevent that, , etc. What I typically do is determine a baseline increase I can give everyone to offset inflation (tough this year!) and then work out what discretionary amount I am left with. In the above example, I might 'spend' $75,000 on small increments for everyone, and then have $25,000 left to split out as I see fit, based on performance, taking on responsibility, and to bring up people who were bad at their initial negotiations, and are basically underpaid.
In rough terms, the company I work for is listed on the stock exchange, and numbers approximately 1000 people.