OK, found a more complete workaround for decent browsers (latest IE9) that allows per-column styling. It is based on passing values in rarely-used CSS properties and CSS3 nth-child property.<br>
First, we need to agree that our ticket report might sound bad if pronounced by text-to-speech software. Then we can use the 'elevation' property for our own purposes. 'elevation: 1deg;' will be a substitute for 'class=myclass1', 'elevation: 2deg;' for 'class=myclass2', etc.<br>
<br>
WHEN status='CLOSED' AND severity='HIGH' THEN '#909090; elevation: 1deg;'<br>
WHEN status='CLOSED' THEN '#909090; elevation: 2deg;'<br>
<br>
Note the spaces after the first semicolon and after the 'elevation:' property, and the trailing semicolon.<br>
Then, in CSS<br>
<br>
table.report tr[style~="1deg;"] td:nth-child(1) {<br>
  text-decoration: line-through;<br>
}<br>
<br>
Again, note the trailing semicolon and lack of the property name in the selector. We need to follow this syntax because a) attribute text is space-separated in ~= matches, and b) some browsers internally rewrite CSS into this 'canonical' form.<br>
These settings strike out the numbers of the closed highly-severe tickets, but leave other columns intact. Background color of all closed tickets is the same.<br>
Unfortunately, IE7-8 does not support this.