I think we can all agree that many of these third party partnerships and time exclusivity in Microsoft and Sony's E3 conference really show and reminds us how important 3rd parties are in this game industry.
Just take a look at these huge third party games that have been partnered or bought for time exclusivity between MS and Sony:
Tomb Raider
Final Fantasy 7
Shemue 3
Fallout IV
COD: BLOPS3
Assassin Creed
Destiny
etc
with Final Fantasy 7 and Shemue 3 stealing the show today.
One can even argue that Monster Hunter exclusivity on 3DS sealed PSVita's faith in the dedicated handheld market as well.
Third parties dominance and importance never seem to be this big except maybe the 6th gen (PS2 era).
Out of the three platform makers, Sony will most likely win E3, but I think the real winners this E3 are the 3rd parties.