That's not how it works now. The three division winners are only guaranteed a top 4 seed, not a top 3. A non-division winner can be as high as #2 in the conference, if the top 2 teams in the conference come from the same division. In our case, if (as seems likely) Boston ends up #1 in the East again while Cleveland stays ahead of the Pistons in the Central, the Pistons can still get the 3 seed if they finish with a better record than whoever wins the Southeast (i.e. they would need to finish ahead of both Orlando and Atlanta).