I would cite two main reasons.
First, as you hinted in your opening post, it is the first time that we see a Legolas "stunt", so it doesn't stand out particularly in the scheme of things.
Secondly, it is more in keeping with Legolas' nature as an agile Elven warrior. The shield surfing (which I don't like) and the Oliphaunt climbing (to a lesser extent, in my opinion) are more likely to "break the spell" and take us out of the story because they are less in keeping with the Legolas we know from the book and also, possibly, because we are catching on that Legolas "stunts" are becoming "set-piece" features of the films.
I would note that another Legolas moment that seems to attract little criticism is his twisting leap onto the back of his moving horse, although I still maintain that it was an anatomically impossible feat.
