Two issues. 

The first is that pruning results in almost the exact same savings and is optional.

The second is how do you ensure the summary is accurate?  To verify the summary requires having all prior blocks anyways.

The reality is that over time MOST users will use lightweight clients which don't have the blockchain at all.  The nodes which do keep the blockchain (miners, paranoid users, banks, exchanges, merchants, service providers, etc) will want full functionality.