A few of the differences between HS2 and HS1. The developers of HS2 are ignoring the lessons learnt and experience gained from developing HS1.
Early plans for HS1 intended to use the North London Line to run Eurostar trains from St Pancras onto the West Coast Main Line, so services could run from the Continent to Milton Keynes, Birmingham, and beyond. However, it was not possible to make the necessary alterations to the North London Line so the link from HS1 to the West Coast Main Line was dropped.
The HS2 proposal was initially put forward by the last Labour government with no link to HS1 and when the Coalition came into government, they tried to correct this. Again it was proposed to use the North London Line for high speed trains and again it has proved to be impossible. Similarly, HS2 does not have a connection to Heathrow or any other London airport.
This all shows that HS2 has not been developed to be part of a high speed network but with a shortsighted view of simply duplicating parts of the existing rail network.
This is very different design viewpoint to HS1. HS1 was an entirely new route to the Channel Tunnel, and made St Pancras a new and viable destination for commuters from Kent.