Thats a really difficult subject. Every point has its pro and cons.
Although you should know what you need to run a webserver not every one does. So per se it's nothing wrong to have packages following the credo everything you need will be installed. Further it allows new users to have a quick look into the system. Anyway in the current state the packages prefer given components like Apache, which may not be needed for everyone.
On the other hand it could come in handy to have multiple packages with different applications. But as you can easily see there are a whole bunch of combinations possible apache+postfix or exim lighttp+postfix and so on (hope that i didn't messed anything around). So without good automation package creation can become a pain and time killer (and the devs are already short in time). Neither do i know if the package creation is always possible without problems, which is another point against such a package diversity.
What I would prefer is to drop all requirements and simply install a plain Froxlor. Maybe an Installer script could be written which guides the user to package install process where he can choose between the possible combinations (just like the discussion in this thread: http://forum.froxlor.org/index.php?/topic/1322-improving-the-froxlor-server-installation-process/).
I think this is the right way as with a more modular froxlor, you may have to install, cause of some module, other applications by hand anyway. So why not behave like this from the start. Indeed it would be needed to expand corresponding howtos.