I fully agree. If your site is a non-commercial site, what harm is there in crediting the tools? You will actually be helping yourself by leaving them. The support that those links attracts can only help improve the tools.
Of course if your web site is commercial, the tools are a distraction that you will want to remove. In which case, the least you can do is give the developer a few bucks.
This theme is obviously the work of hundreds of hours. The quality is high. The creativity is immeasurable.