I've spent most of my career working at large Web-focused companies which typically have multiple Web development teams to handle their sites. While the Web may be the vehicle that makes their business viable, most of the business people in these companies are
ignorant oblivious too busy to follow the developments of the browser market space.
These companies, while all different, handled the release of new browsers using the same wait-and-see approach: wait until the browser comes out, see how much of the site's traffic moves to that browser, then invest on bug-fixing only if n% of users are on that browser. Most, if not all, of the alpha/beta/RC testing was done by developers who were interested enough to test and possibly bug fix (assuming the issues weren't major shared template problems). And they were probably doing this on their own time, because the business wasn't going to stop business-supporting, revenue-generating development work in order to support a new browser!
I often owned the browser support matrix at the companies I worked for, but just because I owned it didn't mean I could change it whenever I wanted. I had to convince the business teams that preparing for a new browser was worth our time and money. If I didn't walk into meetings with current and historical browser usage statistics and demonstrations of bugs in the new browser, I would have been laughed out of the room. Simply stating that "a new browser is coming and we'd better be ready" just wasn't, and isn't, enough.
Other than a handful of companies, businesses aren't in the browser business, or even in the browser support business (even though we developers may feel differently). Microsoft is right to not expect all businesses and Web sites to jump just because they have a new browser coming out, and I think that IE8's Compatibility Mode provides a decent solution to bridging the gap for users between the old, crappily coded sites and the nice, new(er), standards-compliant sites.
I'm not jumping for joy over it, of course, because it signals that we standardistas haven't succeeded in our education mission. There still aren't enough designers and developers out there building standards-compliant Web sites, with or without business support, to withstand an event such as this. There certainly aren't enough business people who understand the Web well enough to simplify the business case for standards-based development. Community and education tie into this as well.
Those who think that IE8 is going to be a wake-up call to businesses dependent on the Web are wrong -- it won't be. But it should be one to all of those designers and developers and business people who do understand the benefits of sticking with the standards: we still need to get out there and talk to our colleagues and community about standards, and help move the Web forward!