You can query the number of columns on a particular row. This would be more general and allow for say 2 or 3 columns to be merged together. Also, I think this foreach type of loop will be faster than your while because the fancy object method $table->Rows->Count is only evaluated once and not on every loop iteration.

# Iterate through rows and count columns
foreach my $row_index (1 .. $table->Rows->Count) {
    my $row = $table->Rows->Item($row_index);
    my $column_count = $row->Cells->Count;
    print "Row $row_index has $column_count columns.\n";
}
[download]

posting quickly because the website is unstable and I am getting timeouts when loading pages