This what I think. Take of it what you want. I do not doubt that using the top sider is better IF and only IF you only have aboout 30 minutes to change the oil. I suspect that is why the dealer do it this way.
Like Larry said, oil is very clingy. It takes a while for it to travel down. So, unless you topside at night and then topside in the morning, Larry's method I believe is the best method. After all, the dealer is not going to leave a bunch of cars overnight to get the oil out.
my 2 cents...