What's the difference between .zip and .exe from download site?

[David Chen]

Hi, there:
 
I tried both .zip and .exe to install tomcat on my Win2000 box. It seems
that for .exe: a. it installed Tomcat as win service; b. it also created
some registry keys about TomCat version, etc. (Which is critical, I guess,
for other applications to check TomCat version, right?). Anything else
besides?
So, then what is that .zip download for? In which scenarios we should use
.zip instead of .exe to install TomCat on Windows system? 
 
Thanks a lot
David