These tutorials focus mainly on OpenGL, Win32 programming and the ODE physics engine. OpenGL has moved on to great heights and I don't cover the newest features but cover all of the basic concepts you will need with working example programs.
Working with the Win32 API is a great way to get to the heart of Windows and is just as relevant today as ever before. Whereas ODE has been marginalized as hardware accelerated physics becomes more common.
Games and graphics utilities can be made quickly and easily using game engines like Unity so this and Linux development in general will be the focus of my next tutorials.
Q. Is it wrong to use code from other people's work in our own programs?
A. Not if the copyright allows it.
Gone are the days of the die-hard programmer that made every part of their programs from the ground up. We do not want to spend programming time "re-inventing the wheel" which is why we use Win32, OpenGL and other API's to do most of the things that early programmers had to do themselves.
One analogy is that of building a car. If we were to build a car we would almost certainly not begin by mining the iron ore needed to build the chassis, engine block, panels, etc. We would buy the metal from a supplier or recycle some unwanted metal. A more prudent person would skip the casting of the parts and concern himself with finding the best parts from which to assemble his car.
Companies buy/franchise code all the time and this speeds up their development times greatly. We poorer/independent developers will have to make do with what little is available to us through the generosity of other programmers. The future of game development will most likely be held by programmers who, rather than being mathematical/programming experts, are best able to comprehend other programmers work and judge its suitability for the task as well as their ability to incorporate it into their own programs.