Perhaps hardware companies don't have the "dropbox" effect of such quick growth. Do you think though that hardware companies may be a less risky proposition in some ways?
For example they are less likely to have the sort of network effects problem that some social media based application would.
Of all the companies they are funding, I could totally see Lockitron going viral. Once you have the app on your phone, you have the first key in your keychain. Once the price drops to like $50 a unit, you are in the realm of being super competitive with your standard physical lock, enough so that people would start looking at each key on their keychain as one that can be replaced.
For example they are less likely to have the sort of network effects problem that some social media based application would.