Ahh, give and take. For-each is given nodes and apply-templates takes
nodes it "wants". I think I see.

Well the answer I look for is that with xsl:apply-templates the
processing is controlled by the structure of the input document, while
with xsl:for-each the processing is controlled by the stylesheet.  If
you understand and can describe what happens when you call
<xsl:apply-templates/> then you're doing better than most.