What makes you so confident that they have the expertise to do so?
I don't mean to be nasty about this, but if there is one thing Apple has consistently shown they do not understand it's networked infrastructure. iTunes has been plagued with problems for years. iDisk is unreliable, MobileMe was a disaster, WebObjects was a framework nearly universally rejected, the apple store has to close its curtains for inventory updates (wtf? It's 2011, Apple), Back To My Mac has never worked well (when it works at all), Apple's streaming video servers frequently have problems that put AppleTVs in bad states (restart required, sorry!), and OSX Server has never been a robust platform for infrastructure.
All the evidence suggests that this is Apple's big weakness. pointing this out isn't being unfair; it's being legitimately worried about their ability to execute on iCloud. No one worries if Apple can execute on the mobile or user-facing software side of the plan, because they've consistently shown they can execute there.