You are not wrong, there is overlap and blurred lines between many Stack ExchangeStack Exchange sites.
I suspect I could find some overlap in questions that might be somewhat on-topic on Webmasters that could be asked on many other sites includingdrupal, wordpress, sharepoint, stackoverflow, serverfault, database admins, writers, it security, graphic design, interface design, programmers, ubuntu, linux/unix, video production.
There is also lots of webmaster things we don't want on serverfault.
Serverfault was the second site, right after stackoverflow, followed by Superuser. Yes, serverfault has more questions, and shows up in Google more often. But people should take the time to find the best place to ask your question, not just pick the first place were it won't be immediately flagged as off-topic.
See the very first point under the 'when you ask' section of How To Ask Questions The Smart Way HOWTO.
HackersExperts blow off questions that are inappropriately targeted in order to try to protect their communications channels from being drowned in irrelevance. You don't want this to happen to you.