And by "everyone" you mean who...?
By the numbers, if you total up all women who consider themselves models, and browse many of the modeling sites for their background, you'd find a majority of them specify that they won't do topless, much less nude. Yes, there are many that do, but they're outnumbered.
As I see it, Denise is like a strike of lightning. Out of all the thousands of glamour models who go in and out of the industry each year, she captured enough attention to hit it big and have the following she does. Of course, it's got everything to do with her attractiveness. But if she's finding this kind of success even without baring all, then what incentive does she have to start doing it now? She didn't start out as a nude model, and may never have to become one at this rate. And let's not forget, it may not only be her own standards she's using; she could very well have promised to her family that she'd only do it as a last resort.
Also, about drifter75's comment:
QUOTE:"If she shows them, it will prove they're enhanced and what she's been telling since the beginning that they're natural is just a mean lie and that can end her "career". "
I'm not sure that would happen. Even if Denise does topless at some point, what exactly do you expect to see that would prove they're not natural? We can already see how they sit in bikini tops, and lingerie, all areas exposed except the centers. Just because you'd see the nipples uncovered wouldn't prove anything one way or another. And if you're assuming there'd be scars to see--sure, but only if they aren't photoshopped-out before they're published.
You're right in regard to my previous statement. Personally, I've already spotted the fake symptoms in her boobs, but it would be good to have it clarified officially once forever. And then, let's not be afraid of hitting the ethic aspect of the story: if she made photoshop out the possible scars, what honesty and respect to fans from her could we talk of at all ?