When you're going to try searching for link acquisition in Google, the first results that come out are those that relate to link building. That supports rankwatch.com's reply about link acquisition being a synonym of link building. Well, you can say that it's old, but it's still a term that a lot of people in the SEO world use. It's helpful in such a way that it increases your PageRank, and is a way of building your reputation, if you're using your links as something that would support another content.