Opening apache conf file with write permissions
The reason these applications can't write to that files is to do with application sandboxing feature of OS X, which you can read about here if you are interested.

One GUI application that can write to these files is TextWrangler which you can download for free here. There is also a version of TextWrangler in the Mac App Store (MAS) but it doesn't have the ability to write to system files by default (MAS guidelines don't allow applications with those abilities), but you can find an update here that will update the MAS version of TextWrangler so that it can.

Alternatively you can use command line tools to edit these files. For example sudo nano https.conf works okay, and nano is relatively user friendly.