I'd like to know whether it looks reasonnable to you gurus to write a whole game using the standard memory manager of the operating system
No one can change the standard memory manager of the operating system. The OS mem manager works completely invisible to you.

All you can change is the C Run-Time memory manager, which is very different from the OS mem manager. Paul "Midnight" Nettle ( A guru. A real one, he's worked on "Fly!" ) has an article about that at his column on flipcode that deals with memory managers. It even includes the source code for a sample memory manager created by him ( You can get that at his website too : www.graphicspapers.com , I think )

Custom memory managers help you to debug problems more efficiently ( if you know what you're doing ), and Paul Nettle's is a good example ( it displays debug output on mem leaks, to log files ).