That said, you will not be adding any significant amounts of new muscle while you are dieting down. That is just not the way physiology works. The importance of lifting weights while dieting is simply to give your body a reason to hold on to your existing lean body mass opposed to losing it along with the fat loss you will experience.
I've heard alot of people say similar things, and I agree that you can't really bulk up alot, but there's really no reason why your body cannot get stronger during this time and possibly gain a little bit of muscle size/mass. I've been doing that myself. I weighed in at 155 this morning. 3 months ago I weighed 168 or 169. That's about a pound per week, if not a little more, it's the max recommended rate of loss if you're exercising. Alot of my success is due to exercise, because I'm not even trying to diet anymore, just staying away from sugar and excessive grease.
But anyway, at the start of this time period, I was only cycling occasionally. Due to the bad weather, I started doing other exercises indoors. But, I was rather weak.
When I started, it about killed me to do this:
2 sets of 100 reps of jumping a weighted jump rope, 200 total.
1 set of 10 reps of 185 pounds squatting.
1 set of 25 reps of push-ups
25 crunches
1 set of 8 reps of curls with 50 pounds, with the bar that's 68.
and, well, that's about it.
fast forward 3 months, and I'm now doing:
half an hour of high intensity spinning on my trainer, THEN:
6 sets of 200 reps of weighted jump rope, sometimes doing one-footers... 1,200 total
2 sets of 25 reps of 185 pounds squatting
2 sets of 15 curls with 68 pounds
2 sets of 45 reps of push-ups, even doing them slower with a pause.
65 crunches
25 leg raises
2 sets of 25 reps of leg curls, I forget the weight
I do all of the above in a one hour or so balls-to-the-wall circuit session.
You get the idea. My point is that I have made huge improvements both in weight loss and strength. My abs are showing so much that I started shaving my chest and stomach. I just don't buy the idea that you can't lose weight and build muscle at the same time. True, you can't bulk up a crazy amount, but I don't really want to do that. There's just no way that I could have made the improvements that I have if my body did not have the ability to build muscle. The whole idea behind lifting weights is to break a muscle down, then your body rebuilds, but also overcompensates, and that process is what builds muscles. There's no way that I could have improved so much without the overcompensation part. If my body was simply maintaining itself as was stated, then I should still be doing 25 push-ups then being sore for 2 or 3 days afterwards. Instead, I'm doing 90 total, and could be doing more sets if I wanted... and the next day I'm not sore whatsoever.
So basically, personally, based off of my own results, I believe that you can definitely build muscle while dieting, as long as you eat properly throughout the day, eat properly after a workout for recovery purposes, and consume the right amount of high quality protein. Right now my body is doing far more than just fighting off the "atrophy signals".