L.S.
It's hard to not compare the two babies; however, as you've found out, they each have their own ideas of when they should do things. My son started walking at 10 mos and his cousin (who's a week younger) didnt' start crawling until 12 months or so. In both cases, they were both considered completely within normal limits and the peds were not worried (the same couldn't be said for my SIL though...) Now that they're both two, they both walk and run, etc..
A lot of babies take their time. The good thing about crawling is that it supposedly boosts the brain's power. Talk to your ped at his 12 mos visit.