According to the spec (and this is discutable that's why they added those styles) you have to use portlet-section- for both sections and tables.

Using CSS you can define different styles for:

<span class="portlet-section-header">

and

<th class="portlet-section-header">

I agree that it is not great, i am not sure if we will extend the spec as many did (And is becoming a de-facto standard) or strictly follow the standard (and curiously portlets made for other portals (using portlet-table-* ) won't look the same ....

This in open to discussion.