Finally, I believe this is a solution to a problem that was actually becoming less of a problem since IE7. It is a problem that is going away.
That is what I have assumed is happening. If you build your website today to work in the most standard compliant browsers, and IE8 is so standards compliant, it will work, while IE7 will continue to receive any “fixes” you have had to include (wrapped in lteIE7 conditional comments).
The huge leap forward from IE6 to IE7 means that most sites that will have broken already did. It is very unusual for me to need to add much to an IE7 stylesheet. I assume that an IE8 stylesheet will contain even less.