I owned the Canon 70-200 f/4L IS (just sold it and my 7D to get a D600)... so I can shed some light here. As a primarily landscape shooter the 70-200 f/4L IS was best because:
1. Weight. When backpacking, every ounce makes a difference. On the Canon side the f/4 IS was MUCH smaller and lighter.
2. Don't need f/2.8. If you are mainly shooting landscapes at f/5.6 to f/11 then the added weight of the f/2.8 is unnecessary.
3. Sharp across the frame at every aperture. Just check the MTF charts: http://www.photozone.de/canon_eos_ff/431-canon_70200_4is_5d?start=1
4. 70-200 is just right for telephoto landscape usage: longer leaves out too much...
5. f/4 is still fast enough _outside_ (just one stop... which can be overcome by one stop of ISO) to catch moving things: "Oh shit! Look at that moose running by me!"
6. Weather sealing and ruggedness. The Canon version is built like a tank. It can take drops and can be used in the rain without a worry.
7. IS (VR) is important for handheld landscape shots. In that case, your subject isn't moving, but if the light is a bit poor IS will help more than the one stop you get from a non-IS f/2.8. Yes, I usually shoot from a tripod... but there are times when you can't.
8. Awesome bokeh. The Canon f/4 had super creamy awesome bokeh. Yes, it has less than the f/2.8... but the quality is very nice. Perfect for isolating a fall color tree against it's brethren.
In summary. If you are walking outside the f/4 just made a lot of damn sense. I was sad to sell it... and I'm happy to see that Nikon might be introducing one. If it hits the weight / resolution / $ ratio just right... I'm definitely going to pick one up!