That was the case with sites only working on IE 6. What did you expect?
And after some market share point, it's not about laziness either, it makes business sense to not waste time for a small percentage of users (100% reach is not always better than 90% reach -- there's this thing called "opportunity cost").
This is what we want to avoid.
A lot of companies that thought short term like that our paying through the nose for the decision now because they are still stuck on IE6. There is a business case for avoiding vendor lock in, but it's not quantifiable so it gets ignored.
How many of them will remember the lessons?
Those who forget history are doomed to repeat it.
Not about not caring to test/optimize for other browsers, or using standard stuff some browser gets out faster -- which is what some companies do today with Chrome.
Now with the web, it's much easier to make something work across all platforms, except at the bleeding edge, which is generally where you'll find those sites. Almost all the ones I've seen were tech demos of new browser tech that wasn't available everywhere yet.