Sometimes a cast frame can be better than forged & machined - consider the Browning Hi-Power, where a better alloy and better heat treatment actually improved durability, even though the newer frames are castings.
I'm not entirely sure that the same principle applies to a 1911, but Ruger ought to know how to make a casting work, considering their experience with the process.
I have to wonder about small parts like the ejector, slide stop, thumb safety, hammer, sear, etc. Some of these parts are highly stressed, and at this price point Ruger may not be using forged/machined parts, but cast or MIM components. Maybe they'll hold up . . . we'll see.