Last year's game 1 had a 14 share. The 8.5 you are quoting was the average household rating over all 6 games.
The household rating measures how many total households were tuned in. The share represents the percentage of those watching TV that were tuned in to a particular program.
Here are the ratings for Game 1's in recent years:
2007 ABC Spurs-Cavaliers 5.3/9
2006 ABC Mavericks-Heat 7.8/14
2005 ABC Spurs-Pistons 7.2/13
2004 ABC Lakers-Pistons 9.8/17
2003 ABC Spurs-Nets 6.4/11
2002 NBC Lakers-Nets 10.6/20
2001 NBC Lakers-76ers 12.4/23
2000 NBC Lakers-Pacers 10.5/18
1999 Spurs-Knicks 11.5/21
ABC's best Finals ratings were lower than NBC's worst in the post-Jordan era. And now, in a highly hyped series featuring the chosen one, their ratings not only are down 29% from last year, they are down 26% from the 2005 with less star power, and down 17% from the 2003 series which had no draw whatsoever for the casual fan.
TNT got a 4.9 for Game 6 of the Eastern Conference Finals. On cable. Cleveland against Detroit. ABC, major broadcast network, for the Finals, can only muster a 5.3
While some of this has to do with the country's disinterest in the Spurs, the data point to the spectacular failure of ABC/ESPN to broadcast the NBA in anything approaching a competent fashion.
The NBA's strategy of putting more games on cable assumed that the reduced number of broadcast games would draw more viewers. What David Stern & Co. did not count on was the utter inability of its new broadcast partner to promote the game. I suspect there will be a new strategy for the next TV deal, that will involve a different broadcast partner.