I am not so sure. In the EPL for Liverpool Reina has kept 102 clean sheets in 208 games, which seems pretty impressive given LFC's defensive frailties especially with regard to central defenders (Skrtel, Agger, and that useless Greek bloke), so at United we could probably expect in excess of 20 clean sheets in an EPL season. Sounds good to me.
Silly to underrate Skrtel and Agger as they've had the albatross of bloody Jamie Carragher to perform with - you know, the hoof ball merchant who can barely speak and gets into the team even when he's playing shit (ie. quite regularly).