The Lakers are in the tougher conference and will have played a slightly tougher schedule at the end of the year. Up to this point, the cumulative winning percentage of the Wizards' opponents is .507 (6th in the league), the Lakers is .497 (20th in the league).
So far, the Wizards have a tougher schedule, almost the exact same record, and have been better recently. It might change later, but that's where things stand now.
Nash does make his teammates more efficient on offense. True shooting percentages, years with Nash in Phoenix bolded:
Amare Stoudemire:
2004 - .536
2005 - .617
Joe Johnson:
2002 - .478
2003 - .472
2004 - .491
2005 - .556
2006 - .537
Shawn Marion:
2000 - .511
2001 - .532
2002 - .518
2003 - .538
2004 - .513
2005 - .556
2006 - .591
Quentin Richardson:
2001 - .516
2002 - .534
2003 - .460
2004 - .484
2005 - .522
2006 - .452
Raja Bell:
2002 - .486
2003 - .509
2004 - .500
2005 - .527
2006 - .584
Boris Diaw:
2004 - .483
2005 - .479
2006 - .564
It would be a lot more c/ping, but generally Nash's teammates in Phoenix turn the ball over at a lower rate as well, since he carries so much of the ballhandling responsibility. Bell Marion, Johnson, Diaw, Richardson, Stoudemire all show that effect.
"Making his teammates better" is something a lot of stars get credit for, even when it's obviously not true (Jordan), but in Nash's case, the numbers back it up, and it's easy to see by watching the games. Relatively few Phoenix baskets come from individuals working in the post or off the dribble.
Diaw and Barbosa can create shots at a decent rate, so I think people overrate the role Nash has had in their development, but he's definitely making a huge difference for Stoudemire and Marion (Bell to a slightly lesser degree) by letting them become spot-up shooters or feeding them for easy baskets in the paint.