Performance has changed so much through the centuries. In the baroque era, keyboardists were expected to remain "proper" and polite in performance (except singes, they were the first virtuosos). Keyboard technique was even written down which details proper execution, posture, etc. We have written testament that Clementi, Couperin, Mozart, Cramer, et al of the finger equalization school all sat still while their fingers chopped away at the keys. Then came Beethoven with his Fortes and emotional inflections which he could afford due to the development of the piano in his time. His music marked the beginning of the new era of the piano.
And when the development of the piano reached a new point of evolution, we have Chopin, Thalberg, Liszt, Alkan. Particularly Liszt in his stage mannerisms, but he was not alone in his visual pianistic appeal. But Liszt's music allows great freedom of movement of the other body parts as anyone who has played his works can attest. And this freedom has been abused for more than a century in pianistic showmanship. This showmanship was a direct result of the better pianos of the 19th century.
Into the 20th century, when the piano evolved to its peak, and thus new piano technique began to wane, we entered an area were there was nothing left to say musically. Composers could not write for a better piano because there was none - the piano could do virtually everything with two hands. And hence, the career concert pianist who had no necessity to write music but peform the works of others.
Brahms said he liked to hear his compositions peformed differently each time because he would be bored if they weren't. Perhaps recently, with so much emphasis on the music and less on pianism, performes had to make the same pieces of music attract the audience. But how could they do that? They do it with their faces!

And bodies. This visual attraction changes our perceptions of music events even if it were performed exactly the same way by two different pianists. And they do get the attention.
Does Lang Lang deserve the popularity he recieves when there are many better musicians or does his popularity depend on his showmanship? And Helene Grimaud: why does she perform like a man in her affects and why is she so much more well-known than other better musicians? She certainly is attractive, which sells CDs and tickets (she even posed like a pornstar on one album cover.)