Well Tanya, we're in exactly the same situation here! This little missy is just content to sit on her butt all day if we let her. She loves tummy time, but doesn't show much motivation to move at all, she will spin in circles on her tummy and has just started to push herself backwards in the last few weeks, but there is no trying to lift her belly off the floor at all! Last week I did have her on my bed on her tummy and kind of tickled her side and she did pull her knees under her belly a little and then had traction against the duvet because it's got feather filling to push herself forward. But aside from that - nada!
I spoke to my doctor about it last week when I was there for Nathan and she did a quick assessment as in pulling her up from a lying down position to see if she had good muscle tone and strength and also if she'd bear a little weight on her legs - there was a little there, she won't even attempt to hold onto anything. My doctor said she was developing fine and to give her until 12mths.
Same as you though, it's so different to Nathan who was well on his way to crawling at 7mths and at this age was pulling up to standing. But Danielle will also wave bye bye, say mama and dada to each of us, sign for food, post balls into slots and pump her spinning top toy - Nathan wasn't doing any of these at the same age, so guess he was the little action man and she's developing her verbal/communication and problem solving skills first.
There was a post in this forum a week or so back though with someone's 10.5mth old being referred for physical therapy for not crawling, so not sure if that's standard or not?