fromROSMsg saves an unstructured pointcloud?

edit

When retrieving pointclouds from kinect openni (topic: /camera/rgb/points) and calling

pcl::fromROSMsg(*pcl2_msg_, pcl_xyzrgb_);

the pointcloud goes from structured tu unstructured.

ROS_INFO("msg size %d %d size %d %d ",pcl2_msg_->height, pcl2_msg_->width, (int) pcl_xyzrgb_.height, (int)pcl_xyzrgb_.width);

outputs

[ INFO] [1328803389.512748025]: msg size 480 640 size 1 101595 
[ INFO] [1328803389.945569604]: msg size 480 640 size 1 101593 
[ INFO] [1328803390.400027375]: msg size 480 640 size 1 101676 
[ INFO] [1328803390.840122150]: msg size 480 640 size 1 101569

and so on.

Any hint why this happens and how to keep the pointcloud dense and structured?