I think people are underestimating Cech.
In recent years we've had a keeper or two that have done ok. Nothing special and the odd mistakes though.
A world class goalkeeper however wins you points on his own.
De Gea probably earned united 10 points on his own. Cech can too.
Of course you just have to look at the Chelsea forums to know just how much they rate him (and they do) and they see him a lot more than us.
