It is supposed to be that way http://httpd.apache.org/docs/2.1/platform/windows.html
The main differences in Apache for Windows are:
•Because Apache for Windows is multithreaded, it does not use a separate process for each request, as Apache can on Unix.
Instead there are usually only two Apache processes running: a parent process, and a child which handles the requests. Within the child process each request is handled by a separate thread.
- and it is likely having no effect on your machine, whatever problems it has its probably not the load from httpd.exe - use the Windows Task Mamager to see what processes are using memory and processor cycles.
The only real exception to this might be if you had php scripts that looped or regulalry timed out due to logic errots - BUT they would time out anyway.