I think, for new cyclists and the super obese, the weight comes off more easily with cycling alone, or with cycling/watching what you eat.
As we ride more, and lose more, our bodies change, but we don't always adjust our efforts accordingly.
I know about a year ago, maybe a little more than that, I was in the zone, and got down to 259 I believe, but I stalled there. I tried everything short of joining a gym (couldn't afford it at the time) but I couldn't budge it. Plus, I was ravenously hungry the more I rode.
Like ShartRate (Love the name BTW) says, I'm commuting 24 miles a day when I ride, and on those days I feel like I can't eat enough, but I'm trying hard to limit myself so I do see results.
All that said, based on things I've seen and read here from people who have lost it and kept it off, or kept losing, it's a combination of riding/cardio PLUS weights that pushes them beyond the plateau. I'm hoping to test this theory this winter. I've got the gym membership now.