Going BIG for the Lakers is a gimmick, just like going smalll for the Spurs is. Lakers could have just as easily done it last year, right? I think they do not go to gimmick lineups because it would not work over significant minutes for various reasons.
The good point-forwards have been so venerated historically is because they are rare. Having the best passing and fastest player (pg) on the court against a taller, slower opponent has been proven to be a problem for the latter that is not worth the advantage in height you get from having two SG/sf and no pg's.
This is why the PG position still exists in the NBA. Don't you people think every team would be fielding all 6'6 and taller players on every team otherwise?