I think it's more of a philosophical thing. Apple has the OS set to sleep the MB when the lid is closed. So if you're working on your desk with a MB and an external display, you just close the lid and it goes to sleep.
I can see that some people may want to be able to turn off the MB's LCD when connected to an external, but I guess it's just not something that matches Apple's philosophy.
But at least there's a way to do it ... and honestly, once you've set it up the first time, the MB remembers that the external display is primary, so it's not a big deal later. Just connect the MB to the TV while it's closed/sleeping. Use the remote to wake it up. done. In fact, now that I think about it, you probably don't even need to set the external as the primary as long as you connect the TV while the MB is sleeping.
ft