I have an AdWords ad and a keyword with a Quality Score of 10. Inferring from CPC from actual clicks, max CPC is set way beyond that of the third advertiser from the SERP for this keyword (there are three ads in the top). Still the ad is shown on the 4th spot which located either on the right or at the bottom of the SERP. The only catch is that the ad's status is "under review". Is it the reason why it's blocked from the top spots?
The tentative QS of an ad and keyword don't have much significance, sometimes I'll get a 10, make a few edits and return 15 minutes later and suddenly it's a 4.
Triggering keywords, ad text, landing page, bid and account history (or in this case ad history) all factor in and as noted the review process could too. If the ad is brand new, give it a few days or a week before worrying about it.