I've thought about this but here's the reasoning behind why things are the way they are. There's no such thing as a "disabled" channel, what you're referring to is a channel that has been configured to not update automatically at regular intervals. Hence, when you do an "update all channels", it updates since it's still "active", not "disabled". Now, I could add a switch that marks a channel as "disabled" and never updates but why on earth would someone want to do this? I know I sometimes stay subscribed to blogs that have been abandoned since I want to keep the archived content but updating the feed is harmless since it has no effect. Awasu is an information gathering (and processing) tool, so why would someone want to have a channel but not update it? The only reason I can think of why someone would want to be able to disable channels is if they wanted to update them only manually, but why would you want that? And more to the point, this is such a corner case, is it really worth adding more switches and flags to an already cluttered UI to support it?
Again troubleshooting and trying to find the feed that is clogging the system, and feeds that regularly get errors.
Also, it is pretty time consuming to find out which channels you mistakingly set to full content and keep data months. Maybe a settings report could solve this one.