Really, these "lifestyles" are all estimates. Every body is different and you have to find the one that works best for you. I, too, spend my days in front of a computer with some getting up and walking around (which I try to do as often as possible) so use "seated with some movement".
I do add 8 hours of sleep every day and also add my exercise. For me, this makes the "math" come out pretty close to reality. My burn is around 2800 to 3000 depending upon my exercise for the day and my intake is around 1500 to 1600 which makes my estimated loss around 2.5 to 2.8 pounds a week.
My actual average weekly loss is around 2.75 so pretty darned close!
I do like fairly large calorie deficits just for the reasons you mention. Also, at best, calorie intake and burn are estimates and a razor-thin daily deficit can easily turn into no deficit at all.
If you can comfortably keep at least a 500 cal a day deficit (1,000 is even better) than I think you'd see good results. Of course, you may need to do some fine tuning and your calorie mix may also have some effect on your rate of loss.
47 M 5'8"
May 4, 2010...... 440? lbs. (Start FitDay Size 60 Jeans)
June 19, 2010.... 393 lbs. (First Weigh-in)
June 19, 2011.... 229 lbs. (164 lbs. gone in one year :-)
Current Weight... 185 lbs. (Size 36 Jeans)
Next Goal 169 lbs. (07/04/12)
Ultimate Goal 165 lbs. (12/31/12)
The best exercises for weight loss are Fork Putdowns and Table Pushaways.