Well, a cloud storage is central to the ecosystem they are trying to build, think of Chromebooks. It's not a periferic product like Reader or experiment like Wave.

There is no guarantee of course, in theory it could be replaced by a rebranded product with a completely incompatible API later on; but I doubt it would happen because it looks like Google already went through a spring cleaning of products, with the explicit aim of killing dying, orphaned products in order to strengthen the core products.