So I only really see MythTV as being a replacement PVR - which in a linuxMCE scenario could mean not even having to use the TV button (assuming recording is done via the web based interface).
Why intentionally remove functionality. Since watching "LiveTV" is really just watching the recording, almost immediately after it's recorded, it doesn't make sense to intentionally leave that out. The functionality would have to exist if you are to record anything, so why stop users from accessing it? Personally, I like you don't watch LiveTV very often, but I do from time to time and others in my house do more often. I think that is a more common scenario in the common household with a PVR system.
I think you are in the minority if you want to schedule all your recordings only through the web interface. Although I do use MythWeb to schedule recordings, I don't use it for most. Mythfrontend actually has a very nice interface for this and even allows you to do the "Power Searches" so you can basically schedule anything useing any kind of rule you dream up. I personally use this so I only record my home teams basketball games. Granted that LinuxMCE doesn't have this integrated very well... but that's what this conversation is about.