Having had the experience of a flight of over 200 miles with gear down ina 767 it is extremely noise in the cabin and there was a fair amount of buffeting and shaking too it does seem hard to believe. especially with the landing gear status lights glowing green and in a world of touch screens and dinky switches a relatively big handle thing sticking out in the wrong place.
Just out of interest though why do some airlines have an after take off check list and some don't - certainly after the 737 dead crew incident some years ago it would seem a good practice to double check a few critical items but then no doubt have a good reason for not doing it, not like the crew get paid by the check lists they do is it