Empty button vs button with populated text

Button no text with CSS Backgroup icon

Click the button to display an alert box:

Button no text with CSS Backgroup icon

Click the button to display an alert box:

Results

JAWS 15 or NVDA 2014.2 read it OK in FF and IE, but VoiceOver doesn't read the secont row of TH.

Code

<table width="200" border="1">

<tr>

<td rowspan="2"></td>

<th colspan="2" scope="col">Sales 2013</th>

<th colspan="2" scope="col">Sales 2014</th>

</tr>

<tr>

<th scope="col">Actual</th>

<th scope="col">Budget</th>

<th scope="col">Actual</th>

<th scope="col">Budget</th>

</tr>

<tr>

<th scope="row">Compact cars</th>

<td>$30,000</td>

<td>$50,000</td>

<td>$80,000</td>

<td>$100,000</td>

</tr>

<tr>

<th scope="row">Sedans</th>

<td>$40,000</td>

<td>$60,000</td>

<td>$90,000</td>

<td>$120,000</td>

</tr>

</table>