Why does a filter gradient on a pseudo element not work in IE8?

Question

I want to create buttons like these:

In modern browsers the effect is created using inset box-shadow and filters.
For IE8 - pseudo-elements are chosen.

Answer 1

Rather than using IE's filter style for this, have you considered using CSS3Pie?

This is a script for IE that adds support for standard CSS box-shadow and gradients, so you can write the same code in all browsers rather than having to have all those IE-specific styles.