I think it really depends on a few things; how fast your metabolism naturally is, how old you are, and how much elasticity your skin has (lotions and creams simply cannot prevent stretch marks).
I had my first just after my 21st birthday and all the "damage" was done with her pregnancy/birth; a good amount of stretch marks, though oddly enough none on my belly - though my mom didn't get a single one with any of her 3 babies. My skin never stayed saggy (except after the the first year or so of bf'ing with each of them my boobs are decently deflated and sag quite a bit, but DH doesn't mind so...), but my best friend has crepe-paper-like tummy skin and we're the same age
I did lose a little tone 'down there' after #3, but kegels fixed that. I've never had any trouble losing weight either, I tend to lose a little too much actually.
I do have a little bit of tummy padding even when I'm 120, but it's only like an inch. If I worked out it would probably tone up better.
Anyway, everybody is just different. I do feel 'lucky' I suppose, but I really believe all Mamas are beautiful and think those sites are awesome