Does a supergrid approach confront with distributed generation?
They aim at different goal with the same purpose at the end of the day: having sustainable energy.

Technically speaking, an engineer will evaluate the actual cost of maintaining a long distance generation plant (be it hydroelectric, wind, solar, tidal generator or pretty much anything else). These type of installation will generate a huge sum of energy, but will also require lengthy transmission line, massive infrastructure. 

When you're able to produce electricity locally, you end up having a reduced cost of exploitation because of the small distance and simpler design. However, this will be mostly usable by small industries and housing. 

Combining them together will give a complete flexibility on the grid between local production and state/nation wide supply. 

Interestingly enough, some people are also looking at electric car for other purpose than transportation. They could act like an accumulator and store the excess energy and or release energy into the grid during peak period to smooth out the long distance energy requirement and therefore reducing the losses. A local production will be used in a similar way too. 

Regardless of the actual topology or choice, the bottom line of those technology is a highly heated social debate regarding smart grid, green energy and fossil fuel depletion.