Everything you say is actually wrong.
Seriously, if you don't understand / know something, it's better not to comment and pretend that you do.
No commercial developer develops complex software in C these days...
In retrospect, you'll actually find that most complex software is developed in C, especially operating systems. Windows, linux, osx, bsd, solaris, gnome, Wine, the vast majority of your Windows drivers are written in C, I could go on and on ....
C is far from dead, it's still one of the most widely used languages of today.
Most of Windows I believe nowadays is written in C++. It is simply more productive....
Again, this isn't true. Some high level parts of Windows use C++, like explorer, however most of the operating system (kernel, subsystems, dlls) are written in C and there are good reasons for this.
In the commercial world the reason is money, but for this project I would have thought time...
Contrary to what you think, C is the most productive language to use for this. It's a small language which every programmer worth his salt should know. It's was actually designed for writing operating systems, which aren't meant to be scribbled on the back of a fag packet and thrown together in a 1 month deadline.
You can't compare writing an operating system to developing a web client.
the need to make the most of limited development resources, would be a powerful reason for using RAD tools wherever you could....
RAD tools are all well and good for what they are designed for, I fail to see how this would help. We aren't developing some all singing all dancing GUI application, this is an operating system.
Really, there are a loads of reasons why C is the right language and why everything else isn't. However, I'm not prepared to write a 10 page document on why, if you don't have an understanding of why you'll just have to trust us.
You tell me 1 area of ReactOS which should be developed in a language other than C, and I'll give you the reason(s) why it isn't.