yes, they use the same sensor.
AFAIK, 7D has these improvements over 550D:
- better AF system (manual focus for landscape)
- more FPS (landscape is about 1 click and getting that shot, not run and gun)
- weather sealed body (need weather sealed lens)
- more dials and controls (might make fast adjustments easier, but landscape is not going anywhere)
- IR flash controller (not useful for landscape)
- larger viewfinder, might be helpful for landscape.
Have to add though, I personally would never buy high end stuff. I always buy the cheapest stuff in the best group. eg. full frame would be 6D, crop would be 550D/600D, CPU would be cheapest i7, TV would be cheapest 1080p at the size I want. So I personally see no value in 7D compared to 6D or 5D2, especially for landscape.