National selector Geoff Miller unveiled the hosts' 15-man squad on Friday, with Pietersen already ruled out due to a knee complaint. Joe Root was the principle beneficiary of that as he was named in a batting line-up that contains the likes of Alastair Cook, Ian Bell, Jonathan Trott and Eoin Morgan.
Stewart, who played 133 Tests and 170 ODIs for his country, acknowledges Pietersen's injury is a major blow but sees enough talent in the squad to make up for it, and he told Press Association Sport: "They have other experienced players and it's up to them to show why they've been picked and take the responsibility."
He added: "They're a weaker side without Kevin Pietersen, any team would be.
"He's a match-winner, he's box office and he's done it time and time again in all forms, so of course it's a blow. You can't replace him because he's a one-off cricketer, but they have strength in depth.
"The top three - Alastair Cook, Ian Bell and Jonathan Trott - are all different players and they have a record scoring hundreds. If you score hundreds in a 50-over match, then more often than not you'll win.
"On the flip side you've got Morgan who is a classy player and a finisher who is good under pressure. You need that kind of player too.
"I'd say South Africa will start as favourites but England will be in that next group, among the second, third and fourth favourites. It's a quick tournament and if you get on a roll, you can go and win it."
Stewart also agreed with England's selection of Ravi Bopara as an all-rounder. The Essex man effectively took the place of Samit Patel in the party and Stewart understands the logic.
"They already have Graeme Swann and James Tredwell so you don't need that third spinner, Samit Patel," he said. "He toured over the winter but in England you're more likely to need a sixth bowler who bowls seam or swing like Ravi."
- Sports & Recreation
- Kevin Pietersen
- Jonathan Trott
- Alastair Cook
- Eoin Morgan
- Ian Bell