IE6 usage has nothing to do with technical vs non-technical anymore. Most IE6 usage in the US is due to stupid corporate policies, home users long ago moved on, and of course the current widespread mobile browsers are all way past IE6.

I optimistically hypothesize that users are less likely to access Facebook (or most other non-internal webapps) from a locked-down corporate desktop, and even if not, that those users also access Facebook from non-corporate systems, making the loss of access from the corporate system partly illusory -- if the posited loss is "2%", I think the actual loss is probably as low as 1%.