Well, Tipsy, bootstrap tooltips and similar javascript based tooltips require you to initialize them.

It's fine if you have a mostly static page, so you can initialize all fo them on domready.

But if you are in a very dynamic page with pjax or a Javascript MVC app, you always have to initialize them again on any page change.

It's costly and error prone. This pure CSS solution in the other hand do not require any initialization. You put the HTML with the proper classes and it will just works.