17" notebooks have their place, but they're not the be all end all. When I was working at a fly-in/out jobsite where I'd fly to location, stay there for 3 weeks, then fly home for a week it was great. I'd throw it in a (huge) backpack, hook it up at my desk at camp and it would make my nights less mindnumbingly dull. For daily use though, hauling around a 17" means a huge backpack (or one that doesn't fit much else), and they're not light. Dragging one to university or a job each day, no thanks. I'd rather use something like my Surface where I drag it around easily all day and then hook it up to a bigger monitor when I'm home or at an office. Not to mention the difference in battery life. None of the various ASUS G7XXXX I owned over the years lasted for long just on battery.
13-15" seems a good sweet spot for portability without having a screen so tiny it's painful (or being forced to only have integrated graphics).
If you're only moving the thing once in a blue moon, a 17 is still nice, but with steamboxes and portable monitors becoming more available, they're another option. If MS or Dell/ASUS actually came out with a Surface with thunderbolt and an inexpensive egpu dock/port, I think you'd have a real best of travel/performance option. Drop the heavy kit at your base of operations, and have a reasonably good performing hybrid for on the go that's not so heavy you'll bend sideways dragging it around.