What exactly do you mean by "not working".
The setReadDataOnly(TRUE) option on read doesn't prevent blank cells from being read if the cell actually exists in the spreadsheet file, it simply means that it doesn't read the formatting for any of the cells... a blank cell is still a blank cell, and unless you create a read filter to prevent certain cells from being read, then they will still be loaded.
This behaviour is identical for xls, ods and for xlsx.
The only facility provided in PHPExcel to "skip" blank cells is within the Cell Iterator.