I've noticed this myself quite a bit... In most cases they tend to forget some the most essential components like the PSU, motherboard, and case. The worst of it though, is the people who tend to give out the generalistic lists such as "Well you need ram, a CPU, and a video card." It takes more than finding general components to build a computer. I'm pretty sure you can't just go and stick an Intel Core 2 Duo into a socket designed for an Intel i7, and I also would need to make sure I get a PSU that can handle all the components' electrical needs as well as not going over board and inadvertently wasting power.
Most or almost all motherboards don't have wireless components integrated in, though they do tend to have Audio processors on them now... so a sound card is optional. I can see people forgetting to mention a wireless card as it's also optional, though I think it should be added to any explanation of building a personal computer these days.