That's not actually true. The thing about giants that acquire startups, is that a) they had the resources to build this thing themselves; b) they didn't.
So ask yourself why didn't they build this thing. It wasn't lack of resources. It wasn't lack of intelligence; they keep tabs on everyone and they go to SXSW too. There were forces that stopped the giant from innovating in this direction. Some of them are technological, but the real issues are usually cultural and political.
Once acquired, the startup is now exposed to all these forces -- with double intensity, since it is an outsider and has few friends in the organization. Unless it's already profitable, has a large userbase, or has big fans among the top execs, it has very little power.
I think these recent articles about how giants "ruin" acquisitions do not take culture and politics into account. The technical issues are not the problem.