Unless your route to work is nearly vertical it is extremely unlikely that you burn anywhere near 516 kcal in forty minutes while cycling less than ten miles. I'd suggest that 400 would be an overgenerous estimate. And 80 miles per week is very nice, but unlikely to be enough on its own to generate significant weight loss unless you also pay attention to what you eat - or, more especially, don't eat.

80 miles at moderate pace is probably worth less than one pounds-worth of calories. So if your weight is currently static, and the only thing you change is to add 80 miles per week to the mix, you might expect to see a weight loss of a pound each week, or maybe a bit less. But if you compensate for the activity by eating more, or reward yourself for your endeavours by having a couple more beers, say goodbye to weight loss. The skinny cyclists you see probably do more than 80 miles a week, and do those miles at greater intensity, and are careful about what they eat. Sorry if that is discouraging, but there it is.