I believe the round action is considered stronger than an action based on the Anson & Deeley cocking principle because the action bars are not hollowed out for the cocking levers. With the A&D design a lot of metal is removed from the bars for this purpose.

Here's a photo of an A&D showing the bars and the cocking levers protruding from the front of the bars (in the foreground):

Here's the explanation of strength stated on the David McKay Brown website:

"Strength is obtained by a solid action body with only two small ejector holes. Other actions (side lock) have larger rectangular slots passing through the body."

I don't have a photo of the bars of a Scottish round action, but I know they have small round rods placed near the bottom of the action, just above the trigger plate. These rods do the work of cocking the action.

My $0.02 worth,
Curl