From CNN's live blog [1]:<p><pre><code> Chief Justice John Roberts had noted that however that the
mandate would have been struck down based on the commerce
clause , saying it would "open a new and vast domain" for
Congressional power.
...
Chief Justice John Roberts issued a long opinion in which
he said the controversial individual mandate may be upheld
and is within Congress’ power under the taxing clause
rather than the commerce clause.
</code></pre>
This helped me understand their decision. I'm still not sure what to make of the decision, personally.<p>[1] <a href="http://news.blogs.cnn.com/2012/06/28/how-will-supreme-court-rule-on-health-care-law/?hpt=hp_t1" rel="nofollow">http://news.blogs.cnn.com/2012/06/28/how-will-supreme-court-...</a>