Monitors: Stick to a monitor or get an HDTV?

I'm currently shopping around for a monitor to pair up to my Envy 17 Notebook.
Pricing things around it occurred to me that the size vs price ratio are pretty insane when it comes to monitors.
Yet similarly and even larger sized HDTVs retail for cheaper...
not to mention they have more input choices, higher refresh rates and more real estate...

Which begs the question...
why should I spend upwards $300 on a designated LCD monitor with a 60mhz refresh rate, one HDMI input and one DVI input when I could spend less on a larger LCD HDTV with 120mhz, multiple inputs that I can also use watch TV if I want?

Am I missing something?

Sorry if this has been discussed before, I couldn't really find much about it.