I was surprised to find that Google maps actually seems to work normally in EME with IE 6 under Windows 2000 (I have Windows 2000 on some old test servers). I don’t know why anyone running Windows XP or newer wouldn’t upgrade where upgrades are free and IE 8 is much better, but lots of people seem content to continue using obsolete software.
I host a large number of websites and collect yearly and monthly browser usage statistics based on millions of unique visitors to those sites. The percentage of IE usage during 2010 was as follows:
IE8: 31.32%
IE7: 11.46%
IE6: 17.05%
Note that there was more use of IE6 than IE7.