This is exactly why successful firms spend money not just on headhunting, but on professional development. Many firms will even pay for advanced degrees like MBAs and others, or licenses for more technical work, because they understand the importance of a highly trained workforce.
People are most definitely assets to any organization. No operation is successful without the best people in the right positions. Look at a professional sports team. There they even have legal procedures in place to ensure a fair and balanced process for teams to sign on the most talented players in the nation. In the business world there are head-hunters whose job it is to seek out highly qualified people in a company and then broker deals to have those people be hired at other companies.
The human resources department is a major asset of any company. This department is usually responsible for dealing with the employees and keeping them happy. Often, this department is responsible for screening possible hires. In some cases, they actually do the hiring and firing themselves. They are also responsible for managing the benefits that employees receive. They deal with the legal aspects of employee management as well.
An organization does not actually own its workforce, of course. But the workforce is very important to a company. A company with a highly trained, well-functioning, experienced and stable workforce will have an advantage over a company that does not. So the people who work at a company are really the ones that make it function. They are a company’s greatest asset, more important than real estate or patents. Humans make the company work.
An organization's human resources are absolutely a part of its assets (though not in the technical sense of being put on a balance sheet). Think about a company like Apple. One of its biggest assets is the ability of its workers to be innovative. Therefore, its human resources are a major asset for it.