Yeah, Cambridge in particularly really focus on AS grades, and the CSAT now that UMS has been taken away in England. (The CSAT is the Computer Science Admissions Test).
Having good GCSEs is of course a good thing and will look good on your application, but it's no deal breaker as far as I know. Oxford look more heavily at GCSEs for what it's worth.
I'm not sure they put too much emphasis on predicted grades either as they can be over/underestimations, but they'd probably be looking for you to be predicted to meet their standard offer (A*A*A). If you had a D as a predicted grade in one of your A-levels it would probably hurt your chances quite severely.