Microsoft has posted an explanation on the IE blog on why the company could not drop support on version 6 of its web browser.

The blog notes:
The engineering point of view on IE6 starts as an operating systems supplier. Dropping support for IE6 is not an option because we committed to supporting the IE included with Windows for the lifespan of the product. We keep our commitments. Many people expect what they originally got with their operating system to keep working whatever release cadence particular subsystems have.

Source: Ars Technica