I agree with you that sitting does seem like much harder work than being in the present while I'm walking in the woods or even driving in the car. I also think that you are right that it is more beneficial. I have found that meditation intensives have been really helpful. After a couple of days I seem to finally settle and get into a much deeper stillness.
My own awareness is frequently more difficult to maintain when sitting, as the distractions are mental (shopping lists, my girlfriend arriving in three weeks), not physical (the kettle boiling, the neighbors opening their door). This is what you are describing as well, i think. Yes, more difficult. It's like lifting a hundred pounds instead of fifty, i think, and perhaps more beneficial?
Harry I also see your point. I think our level of awareness does impact the things we do in everyday life. When I am "lost in thought" or not being entirely present I have burned myself baking bread, cut my finger using a knife, almost had a car accident, not to mention being insensitive to those I love, and probably leaving a wake of bad karma without even noticing.
Re. Awareness. I think if people didn't have a certain amount of awareness they would hurt each other and themselves even more than they presently do!: they'd walk in front of cars or drive over each other, walk off the top of buildings, leave their hands in the oven when they make bread, drop litter more, smash windows for the fun of it, be cruel for no reason more... the world would be more "Mad Max"-ish etc. etc. On balance, I'd say people are still more good than bad, more aware of others than deaf to suffering...