Semantically, does the empty row serve a purpose, or is it purely for layout? If the latter, it may be worth considering dropping the empty row, and providing the separation via CSS. E.g.
<tr class="separate-below">
<td>Data before separater</td><td>More Data</td>...
</tr>
<tr>
<td>Data after separater</td><td>More Data</td>...
</tr>
With the following in the stylesheet:
TR.separate-below TD,TR.separate-below TH {
border-bottom: 1em solid white; /* use the background colour of a cell here */
}
Alternatively, you can use multiple <tbody> elements to group blocks of rows together (adding rules="groups" to the table element causes <tbody> elements to gain a horizontal border at top and bottom, and <colgroup> element to gain a border to their left and right):
<table rules="groups">
<thead>
<tr><th>Header</th><th>Header</th>...</tr>
</thead>
<tbody>
<tr><td>Data</td><td>Data</td>...</tr>
<tr><td>Data</td><td>Data</td>...</tr>
...
</tbody>
<tbody>
<tr><td>Data</td><td>Data</td>...</tr>
...
</tbody>
...
</table>