the OP mentioned apple's headaches with the "disappearing" scrollbar, yes I often experienced that in Apple's own site, iTunes Connect (manage App submissions, rejections/comments etc). Disappearing scrollbars on TextArea with large amounts of text made is very easy to miss whole paragraphs of text, can be very costly.

I'm for "Customizing the UI", as long as it helps the User get the most out of the site.